~dkuhlman/python-training-materials/Materials

<h1>16.2. <a class="reference internal" href="#module-io" title="io: Core tools for working with streams."><code class="xref py py-mod docutils literal">io</code></a> — Core tools for working with streams<a class="headerlink" href="#module-io" title="Permalink to this headline">¶</a></h1>

Source code: <a class="reference external" href="https://hg.python.org/cpython/file/3.5/Lib/io.py">Lib/io.py</a>

<h2>16.2.1. Overview<a class="headerlink" href="#overview" title="Permalink to this headline">¶</a></h2>

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The <a class="reference internal" href="#module-io" title="io: Core tools for working with streams."><code class="xref py py-mod docutils literal">io</code></a> module provides Python’s main facilities for dealing with various

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types of I/O. There are three main types of I/O: text I/O, binary I/O

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and raw I/O. These are generic categories, and various backing stores can

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be used for each of them. A concrete object belonging to any of these

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categories is called a <a class="reference internal" href="../glossary.html#term-file-object">file object</a>. Other common terms are stream

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and file-like object.

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Independently of its category, each concrete stream object will also have

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various capabilities: it can be read-only, write-only, or read-write. It can

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also allow arbitrary random access (seeking forwards or backwards to any

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location), or only sequential access (for example in the case of a socket or

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pipe).

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All streams are careful about the type of data you give to them. For example

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giving a <a class="reference internal" href="stdtypes.html#str" title="str"><code class="xref py py-class docutils literal">str</code></a> object to the <code class="docutils literal">write()</code> method of a binary stream

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will raise a <code class="docutils literal">TypeError</code>. So will giving a <a class="reference internal" href="functions.html#bytes" title="bytes"><code class="xref py py-class docutils literal">bytes</code></a> object to the

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<code class="docutils literal">write()</code> method of a text stream.

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Changed in version 3.3: Operations that used to raise <a class="reference internal" href="exceptions.html#IOError" title="IOError"><code class="xref py py-exc docutils literal">IOError</code></a> now raise <a class="reference internal" href="exceptions.html#OSError" title="OSError"><code class="xref py py-exc docutils literal">OSError</code></a>, since

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<a class="reference internal" href="exceptions.html#IOError" title="IOError"><code class="xref py py-exc docutils literal">IOError</code></a> is now an alias of <a class="reference internal" href="exceptions.html#OSError" title="OSError"><code class="xref py py-exc docutils literal">OSError</code></a>.

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</div>

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Text I/O expects and produces <a class="reference internal" href="stdtypes.html#str" title="str"><code class="xref py py-class docutils literal">str</code></a> objects. This means that whenever

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the backing store is natively made of bytes (such as in the case of a file),

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encoding and decoding of data is made transparently as well as optional

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translation of platform-specific newline characters.

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The easiest way to create a text stream is with <a class="reference internal" href="functions.html#open" title="open"><code class="xref py py-meth docutils literal">open()</code></a>, optionally

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specifying an encoding:

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<div class="highlight-python3"><div class="highlight"><pre>f = open("myfile.txt", "r", encoding="utf-8")

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</pre></div>

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</div>

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In-memory text streams are also available as <a class="reference internal" href="#io.StringIO" title="io.StringIO"><code class="xref py py-class docutils literal">StringIO</code></a> objects:

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<div class="highlight-python3"><div class="highlight"><pre>f = io.StringIO("some initial text data")

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</pre></div>

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</div>

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The text stream API is described in detail in the documentation of

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<a class="reference internal" href="#io.TextIOBase" title="io.TextIOBase"><code class="xref py py-class docutils literal">TextIOBase</code></a>.

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</div>

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<h3>16.2.1.2. Binary I/O<a class="headerlink" href="#binary-i-o" title="Permalink to this headline">¶</a></h3>

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Binary I/O (also called buffered I/O) expects

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<a class="reference internal" href="../glossary.html#term-bytes-like-object">bytes-like objects</a> and produces <a class="reference internal" href="functions.html#bytes" title="bytes"><code class="xref py py-class docutils literal">bytes</code></a>

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objects. No encoding, decoding, or newline translation is performed. This

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category of streams can be used for all kinds of non-text data, and also when

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manual control over the handling of text data is desired.

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The easiest way to create a binary stream is with <a class="reference internal" href="functions.html#open" title="open"><code class="xref py py-meth docutils literal">open()</code></a> with <code class="docutils literal">'b'</code> in

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the mode string:

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<div class="highlight-python3"><div class="highlight"><pre>f = open("myfile.jpg", "rb")

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</pre></div>

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</div>

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In-memory binary streams are also available as <a class="reference internal" href="#io.BytesIO" title="io.BytesIO"><code class="xref py py-class docutils literal">BytesIO</code></a> objects:

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<div class="highlight-python3"><div class="highlight"><pre>f = io.BytesIO(b"some initial binary data: \x00\x01")

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</pre></div>

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</div>

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The binary stream API is described in detail in the docs of

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<a class="reference internal" href="#io.BufferedIOBase" title="io.BufferedIOBase"><code class="xref py py-class docutils literal">BufferedIOBase</code></a>.

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Other library modules may provide additional ways to create text or binary

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streams. See <a class="reference internal" href="socket.html#socket.socket.makefile" title="socket.socket.makefile"><code class="xref py py-meth docutils literal">socket.socket.makefile()</code></a> for example.

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</div>

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Raw I/O (also called unbuffered I/O) is generally used as a low-level

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building-block for binary and text streams; it is rarely useful to directly

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manipulate a raw stream from user code. Nevertheless, you can create a raw

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stream by opening a file in binary mode with buffering disabled:

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<div class="highlight-python3"><div class="highlight"><pre>f = open("myfile.jpg", "rb", buffering=0)

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</pre></div>

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</div>

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The raw stream API is described in detail in the docs of <a class="reference internal" href="#io.RawIOBase" title="io.RawIOBase"><code class="xref py py-class docutils literal">RawIOBase</code></a>.

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</div>

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</div>

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<h2>16.2.2. High-level Module Interface<a class="headerlink" href="#high-level-module-interface" title="Permalink to this headline">¶</a></h2>

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<code class="descclassname">io.</code><code class="descname">DEFAULT_BUFFER_SIZE</code><a class="headerlink" href="#io.DEFAULT_BUFFER_SIZE" title="Permalink to this definition">¶</a></dt>

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<dd>An int containing the default buffer size used by the module’s buffered I/O

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classes. <a class="reference internal" href="functions.html#open" title="open"><code class="xref py py-func docutils literal">open()</code></a> uses the file’s blksize (as obtained by

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<a class="reference internal" href="os.html#os.stat" title="os.stat"><code class="xref py py-func docutils literal">os.stat()</code></a>) if possible.

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</dd></dl>

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<code class="descclassname">io.</code><code class="descname">open</code>(file, mode='r', buffering=-1, encoding=None, errors=None, newline=None, closefd=True, opener=None)<a class="headerlink" href="#io.open" title="Permalink to this definition">¶</a></dt>

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<dd>This is an alias for the builtin <a class="reference internal" href="functions.html#open" title="open"><code class="xref py py-func docutils literal">open()</code></a> function.

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</dd></dl>

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exception <code class="descclassname">io.</code><code class="descname">BlockingIOError</code><a class="headerlink" href="#io.BlockingIOError" title="Permalink to this definition">¶</a></dt>

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<dd>This is a compatibility alias for the builtin <a class="reference internal" href="exceptions.html#BlockingIOError" title="BlockingIOError"><code class="xref py py-exc docutils literal">BlockingIOError</code></a>

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exception.

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</dd></dl>

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exception <code class="descclassname">io.</code><code class="descname">UnsupportedOperation</code><a class="headerlink" href="#io.UnsupportedOperation" title="Permalink to this definition">¶</a></dt>

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<dd>An exception inheriting <a class="reference internal" href="exceptions.html#OSError" title="OSError"><code class="xref py py-exc docutils literal">OSError</code></a> and <a class="reference internal" href="exceptions.html#ValueError" title="ValueError"><code class="xref py py-exc docutils literal">ValueError</code></a> that is raised

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when an unsupported operation is called on a stream.

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</dd></dl>

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<h3>16.2.2.1. In-memory streams<a class="headerlink" href="#in-memory-streams" title="Permalink to this headline">¶</a></h3>

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It is also possible to use a <a class="reference internal" href="stdtypes.html#str" title="str"><code class="xref py py-class docutils literal">str</code></a> or <a class="reference internal" href="../glossary.html#term-bytes-like-object">bytes-like object</a> as a

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file for both reading and writing. For strings <a class="reference internal" href="#io.StringIO" title="io.StringIO"><code class="xref py py-class docutils literal">StringIO</code></a> can be used

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like a file opened in text mode. <a class="reference internal" href="#io.BytesIO" title="io.BytesIO"><code class="xref py py-class docutils literal">BytesIO</code></a> can be used like a file

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opened in binary mode. Both provide full read-write capabilities with random

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access.

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See also

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<dd>contains the standard IO streams: <a class="reference internal" href="sys.html#sys.stdin" title="sys.stdin"><code class="xref py py-data docutils literal">sys.stdin</code></a>, <a class="reference internal" href="sys.html#sys.stdout" title="sys.stdout"><code class="xref py py-data docutils literal">sys.stdout</code></a>,

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and <a class="reference internal" href="sys.html#sys.stderr" title="sys.stderr"><code class="xref py py-data docutils literal">sys.stderr</code></a>.</dd>

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</dl>

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</div>

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</div>

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</div>

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<h2>16.2.3. Class hierarchy<a class="headerlink" href="#class-hierarchy" title="Permalink to this headline">¶</a></h2>

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The implementation of I/O streams is organized as a hierarchy of classes. First

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<a class="reference internal" href="../glossary.html#term-abstract-base-class">abstract base classes</a> (ABCs), which are used to

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specify the various categories of streams, then concrete classes providing the

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standard stream implementations.

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Note

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The abstract base classes also provide default implementations of some

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methods in order to help implementation of concrete stream classes. For

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example, <a class="reference internal" href="#io.BufferedIOBase" title="io.BufferedIOBase"><code class="xref py py-class docutils literal">BufferedIOBase</code></a> provides unoptimized implementations of

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<code class="xref py py-meth docutils literal">readinto()</code> and <a class="reference internal" href="#io.IOBase.readline" title="io.IOBase.readline"><code class="xref py py-meth docutils literal">readline()</code></a>.

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</div>

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</div></blockquote>

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At the top of the I/O hierarchy is the abstract base class <a class="reference internal" href="#io.IOBase" title="io.IOBase"><code class="xref py py-class docutils literal">IOBase</code></a>. It

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defines the basic interface to a stream. Note, however, that there is no

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separation between reading and writing to streams; implementations are allowed

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to raise <a class="reference internal" href="#io.UnsupportedOperation" title="io.UnsupportedOperation"><code class="xref py py-exc docutils literal">UnsupportedOperation</code></a> if they do not support a given operation.

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The <a class="reference internal" href="#io.RawIOBase" title="io.RawIOBase"><code class="xref py py-class docutils literal">RawIOBase</code></a> ABC extends <a class="reference internal" href="#io.IOBase" title="io.IOBase"><code class="xref py py-class docutils literal">IOBase</code></a>. It deals with the reading

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and writing of bytes to a stream. <a class="reference internal" href="#io.FileIO" title="io.FileIO"><code class="xref py py-class docutils literal">FileIO</code></a> subclasses <a class="reference internal" href="#io.RawIOBase" title="io.RawIOBase"><code class="xref py py-class docutils literal">RawIOBase</code></a>

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to provide an interface to files in the machine’s file system.

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The <a class="reference internal" href="#io.BufferedIOBase" title="io.BufferedIOBase"><code class="xref py py-class docutils literal">BufferedIOBase</code></a> ABC deals with buffering on a raw byte stream

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(<a class="reference internal" href="#io.RawIOBase" title="io.RawIOBase"><code class="xref py py-class docutils literal">RawIOBase</code></a>). Its subclasses, <a class="reference internal" href="#io.BufferedWriter" title="io.BufferedWriter"><code class="xref py py-class docutils literal">BufferedWriter</code></a>,

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<a class="reference internal" href="#io.BufferedReader" title="io.BufferedReader"><code class="xref py py-class docutils literal">BufferedReader</code></a>, and <a class="reference internal" href="#io.BufferedRWPair" title="io.BufferedRWPair"><code class="xref py py-class docutils literal">BufferedRWPair</code></a> buffer streams that are

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readable, writable, and both readable and writable. <a class="reference internal" href="#io.BufferedRandom" title="io.BufferedRandom"><code class="xref py py-class docutils literal">BufferedRandom</code></a>

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provides a buffered interface to random access streams. Another

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<a class="reference internal" href="#io.BufferedIOBase" title="io.BufferedIOBase"><code class="xref py py-class docutils literal">BufferedIOBase</code></a> subclass, <a class="reference internal" href="#io.BytesIO" title="io.BytesIO"><code class="xref py py-class docutils literal">BytesIO</code></a>, is a stream of in-memory

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bytes.

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The <a class="reference internal" href="#io.TextIOBase" title="io.TextIOBase"><code class="xref py py-class docutils literal">TextIOBase</code></a> ABC, another subclass of <a class="reference internal" href="#io.IOBase" title="io.IOBase"><code class="xref py py-class docutils literal">IOBase</code></a>, deals with

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streams whose bytes represent text, and handles encoding and decoding to and

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from strings. <a class="reference internal" href="#io.TextIOWrapper" title="io.TextIOWrapper"><code class="xref py py-class docutils literal">TextIOWrapper</code></a>, which extends it, is a buffered text

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interface to a buffered raw stream (<a class="reference internal" href="#io.BufferedIOBase" title="io.BufferedIOBase"><code class="xref py py-class docutils literal">BufferedIOBase</code></a>). Finally,

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<a class="reference internal" href="#io.StringIO" title="io.StringIO"><code class="xref py py-class docutils literal">StringIO</code></a> is an in-memory stream for text.

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Argument names are not part of the specification, and only the arguments of

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<a class="reference internal" href="functions.html#open" title="open"><code class="xref py py-func docutils literal">open()</code></a> are intended to be used as keyword arguments.

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The following table summarizes the ABCs provided by the <a class="reference internal" href="#module-io" title="io: Core tools for working with streams."><code class="xref py py-mod docutils literal">io</code></a> module:

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</colgroup>

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<th class="head">Inherits</th>

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<th class="head">Stub Methods</th>

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<th class="head">Mixin Methods and Properties</th>

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</tr>

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</thead>

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<tr class="row-even"><td><a class="reference internal" href="#io.IOBase" title="io.IOBase"><code class="xref py py-class docutils literal">IOBase</code></a></td>

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<td><code class="docutils literal">fileno</code>, <code class="docutils literal">seek</code>,

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and <code class="docutils literal">truncate</code></td>

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<td><code class="docutils literal">close</code>, <code class="docutils literal">closed</code>, <code class="docutils literal">__enter__</code>,

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<code class="docutils literal">__exit__</code>, <code class="docutils literal">flush</code>, <code class="docutils literal">isatty</code>, <code class="docutils literal">__iter__</code>,

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<code class="docutils literal">__next__</code>, <code class="docutils literal">readable</code>, <code class="docutils literal">readline</code>,

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<code class="docutils literal">readlines</code>, <code class="docutils literal">seekable</code>, <code class="docutils literal">tell</code>,

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<code class="docutils literal">writable</code>, and <code class="docutils literal">writelines</code></td>

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</tr>

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<tr class="row-odd"><td><a class="reference internal" href="#io.RawIOBase" title="io.RawIOBase"><code class="xref py py-class docutils literal">RawIOBase</code></a></td>

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<td><a class="reference internal" href="#io.IOBase" title="io.IOBase"><code class="xref py py-class docutils literal">IOBase</code></a></td>

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<td><code class="docutils literal">readinto</code> and

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<code class="docutils literal">write</code></td>

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<td>Inherited <a class="reference internal" href="#io.IOBase" title="io.IOBase"><code class="xref py py-class docutils literal">IOBase</code></a> methods, <code class="docutils literal">read</code>,

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and <code class="docutils literal">readall</code></td>

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</tr>

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<tr class="row-even"><td><a class="reference internal" href="#io.BufferedIOBase" title="io.BufferedIOBase"><code class="xref py py-class docutils literal">BufferedIOBase</code></a></td>

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<td><a class="reference internal" href="#io.IOBase" title="io.IOBase"><code class="xref py py-class docutils literal">IOBase</code></a></td>

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<td><code class="docutils literal">detach</code>, <code class="docutils literal">read</code>,

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<code class="docutils literal">read1</code>, and <code class="docutils literal">write</code></td>

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</tr>

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<tr class="row-odd"><td><a class="reference internal" href="#io.TextIOBase" title="io.TextIOBase"><code class="xref py py-class docutils literal">TextIOBase</code></a></td>

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<td><a class="reference internal" href="#io.IOBase" title="io.IOBase"><code class="xref py py-class docutils literal">IOBase</code></a></td>

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<td><code class="docutils literal">detach</code>, <code class="docutils literal">read</code>,

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<code class="docutils literal">readline</code>, and

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<code class="docutils literal">write</code></td>

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<code class="docutils literal">errors</code>, and <code class="docutils literal">newlines</code></td>

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</tr>

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</tbody>

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</table>

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<h3>16.2.3.1. I/O Base Classes<a class="headerlink" href="#i-o-base-classes" title="Permalink to this headline">¶</a></h3>

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class <code class="descclassname">io.</code><code class="descname">IOBase</code><a class="headerlink" href="#io.IOBase" title="Permalink to this definition">¶</a></dt>

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<dd>The abstract base class for all I/O classes, acting on streams of bytes.

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There is no public constructor.

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This class provides empty abstract implementations for many methods

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that derived classes can override selectively; the default

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implementations represent a file that cannot be read, written or

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seeked.

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Even though <a class="reference internal" href="#io.IOBase" title="io.IOBase"><code class="xref py py-class docutils literal">IOBase</code></a> does not declare <code class="xref py py-meth docutils literal">read()</code>, <code class="xref py py-meth docutils literal">readinto()</code>,

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or <code class="xref py py-meth docutils literal">write()</code> because their signatures will vary, implementations and

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clients should consider those methods part of the interface. Also,

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implementations may raise a <a class="reference internal" href="exceptions.html#ValueError" title="ValueError"><code class="xref py py-exc docutils literal">ValueError</code></a> (or <a class="reference internal" href="#io.UnsupportedOperation" title="io.UnsupportedOperation"><code class="xref py py-exc docutils literal">UnsupportedOperation</code></a>)

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when operations they do not support are called.

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The basic type used for binary data read from or written to a file is

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<a class="reference internal" href="functions.html#bytes" title="bytes"><code class="xref py py-class docutils literal">bytes</code></a>. Other <a class="reference internal" href="../glossary.html#term-bytes-like-object">bytes-like objects</a> are

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accepted as method arguments too. In some cases, such as

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<a class="reference internal" href="#io.RawIOBase.readinto" title="io.RawIOBase.readinto"><code class="xref py py-meth docutils literal">readinto()</code></a>, a writable object such as <a class="reference internal" href="functions.html#bytearray" title="bytearray"><code class="xref py py-class docutils literal">bytearray</code></a>

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is required. Text I/O classes work with <a class="reference internal" href="stdtypes.html#str" title="str"><code class="xref py py-class docutils literal">str</code></a> data.

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Note that calling any method (even inquiries) on a closed stream is

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undefined. Implementations may raise <a class="reference internal" href="exceptions.html#ValueError" title="ValueError"><code class="xref py py-exc docutils literal">ValueError</code></a> in this case.

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<a class="reference internal" href="#io.IOBase" title="io.IOBase"><code class="xref py py-class docutils literal">IOBase</code></a> (and its subclasses) supports the iterator protocol, meaning

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that an <a class="reference internal" href="#io.IOBase" title="io.IOBase"><code class="xref py py-class docutils literal">IOBase</code></a> object can be iterated over yielding the lines in a

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stream. Lines are defined slightly differently depending on whether the

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stream is a binary stream (yielding bytes), or a text stream (yielding

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character strings). See <a class="reference internal" href="#io.IOBase.readline" title="io.IOBase.readline"><code class="xref py py-meth docutils literal">readline()</code></a> below.

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<a class="reference internal" href="#io.IOBase" title="io.IOBase"><code class="xref py py-class docutils literal">IOBase</code></a> is also a context manager and therefore supports the

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<a class="reference internal" href="../reference/compound_stmts.html#with"><code class="xref std std-keyword docutils literal">with</code></a> statement. In this example, file is closed after the

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<a class="reference internal" href="../reference/compound_stmts.html#with"><code class="xref std std-keyword docutils literal">with</code></a> statement’s suite is finished—even if an exception occurs:

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<div class="highlight-python3"><div class="highlight"><pre>with open('spam.txt', 'w') as file:

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file.write('Spam and eggs!')

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</pre></div>

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</div>

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<a class="reference internal" href="#io.IOBase" title="io.IOBase"><code class="xref py py-class docutils literal">IOBase</code></a> provides these data attributes and methods:

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<code class="descname">close</code>()<a class="headerlink" href="#io.IOBase.close" title="Permalink to this definition">¶</a></dt>

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<dd>Flush and close this stream. This method has no effect if the file is

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already closed. Once the file is closed, any operation on the file

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(e.g. reading or writing) will raise a <a class="reference internal" href="exceptions.html#ValueError" title="ValueError"><code class="xref py py-exc docutils literal">ValueError</code></a>.

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As a convenience, it is allowed to call this method more than once;

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only the first call, however, will have an effect.

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</dd></dl>

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<code class="descname">closed</code><a class="headerlink" href="#io.IOBase.closed" title="Permalink to this definition">¶</a></dt>

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<dd><code class="docutils literal">True</code> if the stream is closed.

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</dd></dl>

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<code class="descname">fileno</code>()<a class="headerlink" href="#io.IOBase.fileno" title="Permalink to this definition">¶</a></dt>

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<dd>Return the underlying file descriptor (an integer) of the stream if it

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exists. An <a class="reference internal" href="exceptions.html#OSError" title="OSError"><code class="xref py py-exc docutils literal">OSError</code></a> is raised if the IO object does not use a file

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descriptor.

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</dd></dl>

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<code class="descname">flush</code>()<a class="headerlink" href="#io.IOBase.flush" title="Permalink to this definition">¶</a></dt>

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<dd>Flush the write buffers of the stream if applicable. This does nothing

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for read-only and non-blocking streams.

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</dd></dl>

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<code class="descname">isatty</code>()<a class="headerlink" href="#io.IOBase.isatty" title="Permalink to this definition">¶</a></dt>

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<dd>Return <code class="docutils literal">True</code> if the stream is interactive (i.e., connected to

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a terminal/tty device).

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</dd></dl>

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<code class="descname">readable</code>()<a class="headerlink" href="#io.IOBase.readable" title="Permalink to this definition">¶</a></dt>

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<dd>Return <code class="docutils literal">True</code> if the stream can be read from. If <code class="docutils literal">False</code>, <code class="xref py py-meth docutils literal">read()</code>

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will raise <a class="reference internal" href="exceptions.html#OSError" title="OSError"><code class="xref py py-exc docutils literal">OSError</code></a>.

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</dd></dl>

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<code class="descname">readline</code>(size=-1)<a class="headerlink" href="#io.IOBase.readline" title="Permalink to this definition">¶</a></dt>

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<dd>Read and return one line from the stream. If size is specified, at

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most size bytes will be read.

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The line terminator is always <code class="docutils literal">b'\n'</code> for binary files; for text files,

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the newline argument to <a class="reference internal" href="functions.html#open" title="open"><code class="xref py py-func docutils literal">open()</code></a> can be used to select the line

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terminator(s) recognized.

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</dd></dl>

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<code class="descname">readlines</code>(hint=-1)<a class="headerlink" href="#io.IOBase.readlines" title="Permalink to this definition">¶</a></dt>

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<dd>Read and return a list of lines from the stream. hint can be specified

397

to control the number of lines read: no more lines will be read if the

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total size (in bytes/characters) of all lines so far exceeds hint.

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Note that it’s already possible to iterate on file objects using <code class="docutils literal">for

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line in file: ...</code> without calling <code class="docutils literal">file.readlines()</code>.

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</dd></dl>

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<code class="descname">seek</code>(offset[, whence])<a class="headerlink" href="#io.IOBase.seek" title="Permalink to this definition">¶</a></dt>

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<dd>Change the stream position to the given byte offset. offset is

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interpreted relative to the position indicated by whence. The default

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value for whence is <code class="xref py py-data docutils literal">SEEK_SET</code>. Values for whence are:

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<li><code class="xref py py-data docutils literal">SEEK_SET</code> or <code class="docutils literal">0</code> – start of the stream (the default);

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offset should be zero or positive</li>

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<li><code class="xref py py-data docutils literal">SEEK_CUR</code> or <code class="docutils literal">1</code> – current stream position; offset may

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be negative</li>

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<li><code class="xref py py-data docutils literal">SEEK_END</code> or <code class="docutils literal">2</code> – end of the stream; offset is usually

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negative</li>

416

</ul>

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Return the new absolute position.

418

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New in version 3.1: The <code class="docutils literal">SEEK_*</code> constants.

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</div>

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New in version 3.3: Some operating systems could support additional values, like

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<code class="xref py py-data docutils literal">os.SEEK_HOLE</code> or <code class="xref py py-data docutils literal">os.SEEK_DATA</code>. The valid values

424

for a file could depend on it being open in text or binary mode.

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</div>

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</dd></dl>

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<code class="descname">seekable</code>()<a class="headerlink" href="#io.IOBase.seekable" title="Permalink to this definition">¶</a></dt>

431

<dd>Return <code class="docutils literal">True</code> if the stream supports random access. If <code class="docutils literal">False</code>,

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<a class="reference internal" href="#io.IOBase.seek" title="io.IOBase.seek"><code class="xref py py-meth docutils literal">seek()</code></a>, <a class="reference internal" href="#io.IOBase.tell" title="io.IOBase.tell"><code class="xref py py-meth docutils literal">tell()</code></a> and <a class="reference internal" href="#io.IOBase.truncate" title="io.IOBase.truncate"><code class="xref py py-meth docutils literal">truncate()</code></a> will raise <a class="reference internal" href="exceptions.html#OSError" title="OSError"><code class="xref py py-exc docutils literal">OSError</code></a>.

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</dd></dl>

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<dd>Return the current stream position.

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</dd></dl>

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<code class="descname">truncate</code>(size=None)<a class="headerlink" href="#io.IOBase.truncate" title="Permalink to this definition">¶</a></dt>

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<dd>Resize the stream to the given size in bytes (or the current position

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if size is not specified). The current stream position isn’t changed.

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This resizing can extend or reduce the current file size. In case of

447

extension, the contents of the new file area depend on the platform

448

(on most systems, additional bytes are zero-filled). The new file size

449

is returned.

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</dd></dl>

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Changed in version 3.5: Windows will now zero-fill files when extending.

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</div>

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<code class="descname">writable</code>()<a class="headerlink" href="#io.IOBase.writable" title="Permalink to this definition">¶</a></dt>

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<dd>Return <code class="docutils literal">True</code> if the stream supports writing. If <code class="docutils literal">False</code>,

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<code class="xref py py-meth docutils literal">write()</code> and <a class="reference internal" href="#io.IOBase.truncate" title="io.IOBase.truncate"><code class="xref py py-meth docutils literal">truncate()</code></a> will raise <a class="reference internal" href="exceptions.html#OSError" title="OSError"><code class="xref py py-exc docutils literal">OSError</code></a>.

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</dd></dl>

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<code class="descname">writelines</code>(lines)<a class="headerlink" href="#io.IOBase.writelines" title="Permalink to this definition">¶</a></dt>

465

<dd>Write a list of lines to the stream. Line separators are not added, so it

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is usual for each of the lines provided to have a line separator at the

467

end.

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</dd></dl>

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<dd>Prepare for object destruction. <a class="reference internal" href="#io.IOBase" title="io.IOBase"><code class="xref py py-class docutils literal">IOBase</code></a> provides a default

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implementation of this method that calls the instance’s

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<a class="reference internal" href="#io.IOBase.close" title="io.IOBase.close"><code class="xref py py-meth docutils literal">close()</code></a> method.

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</dd></dl>

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</dd></dl>

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class <code class="descclassname">io.</code><code class="descname">RawIOBase</code><a class="headerlink" href="#io.RawIOBase" title="Permalink to this definition">¶</a></dt>

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<dd>Base class for raw binary I/O. It inherits <a class="reference internal" href="#io.IOBase" title="io.IOBase"><code class="xref py py-class docutils literal">IOBase</code></a>. There is no

484

public constructor.

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Raw binary I/O typically provides low-level access to an underlying OS

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device or API, and does not try to encapsulate it in high-level primitives

487

(this is left to Buffered I/O and Text I/O, described later in this page).

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In addition to the attributes and methods from <a class="reference internal" href="#io.IOBase" title="io.IOBase"><code class="xref py py-class docutils literal">IOBase</code></a>,

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<dd>Read up to size bytes from the object and return them. As a convenience,

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if size is unspecified or -1, <a class="reference internal" href="#io.RawIOBase.readall" title="io.RawIOBase.readall"><code class="xref py py-meth docutils literal">readall()</code></a> is called. Otherwise,

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only one system call is ever made. Fewer than size bytes may be

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returned if the operating system call returns fewer than size bytes.

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If 0 bytes are returned, and size was not 0, this indicates end of file.

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If the object is in non-blocking mode and no bytes are available,

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<code class="docutils literal">None</code> is returned.

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</dd></dl>

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<code class="descname">readall</code>()<a class="headerlink" href="#io.RawIOBase.readall" title="Permalink to this definition">¶</a></dt>

505

<dd>Read and return all the bytes from the stream until EOF, using multiple

506

calls to the stream if necessary.

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</dd></dl>

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510

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<code class="descname">readinto</code>(b)<a class="headerlink" href="#io.RawIOBase.readinto" title="Permalink to this definition">¶</a></dt>

512

<dd>Read bytes into a pre-allocated, writable

513

<a class="reference internal" href="../glossary.html#term-bytes-like-object">bytes-like object</a> b, and return the

514

number of bytes read. If the object is in non-blocking mode and no bytes

515

are available, <code class="docutils literal">None</code> is returned.

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</dd></dl>

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<code class="descname">write</code>(b)<a class="headerlink" href="#io.RawIOBase.write" title="Permalink to this definition">¶</a></dt>

521

<dd>Write the given <a class="reference internal" href="../glossary.html#term-bytes-like-object">bytes-like object</a>, b, to the

522

underlying raw stream, and return the number of

523

bytes written. This can be less than the length of b in

524

bytes, depending on specifics of the underlying raw

525

stream, and especially if it is in non-blocking mode. <code class="docutils literal">None</code> is

526

returned if the raw stream is set not to block and no single byte could

527

be readily written to it. The caller may release or mutate b after

528

this method returns, so the implementation should only access b

529

during the method call.

530

</dd></dl>

531

532

</dd></dl>

533

534

535

536

class <code class="descclassname">io.</code><code class="descname">BufferedIOBase</code><a class="headerlink" href="#io.BufferedIOBase" title="Permalink to this definition">¶</a></dt>

537

<dd>Base class for binary streams that support some kind of buffering.

538

It inherits <a class="reference internal" href="#io.IOBase" title="io.IOBase"><code class="xref py py-class docutils literal">IOBase</code></a>. There is no public constructor.

539

The main difference with <a class="reference internal" href="#io.RawIOBase" title="io.RawIOBase"><code class="xref py py-class docutils literal">RawIOBase</code></a> is that methods <a class="reference internal" href="#io.BufferedIOBase.read" title="io.BufferedIOBase.read"><code class="xref py py-meth docutils literal">read()</code></a>,

540

<a class="reference internal" href="#io.BufferedIOBase.readinto" title="io.BufferedIOBase.readinto"><code class="xref py py-meth docutils literal">readinto()</code></a> and <a class="reference internal" href="#io.BufferedIOBase.write" title="io.BufferedIOBase.write"><code class="xref py py-meth docutils literal">write()</code></a> will try (respectively) to read as much

541

input as requested or to consume all given output, at the expense of

542

making perhaps more than one system call.

543

In addition, those methods can raise <a class="reference internal" href="exceptions.html#BlockingIOError" title="BlockingIOError"><code class="xref py py-exc docutils literal">BlockingIOError</code></a> if the

544

underlying raw stream is in non-blocking mode and cannot take or give

545

enough data; unlike their <a class="reference internal" href="#io.RawIOBase" title="io.RawIOBase"><code class="xref py py-class docutils literal">RawIOBase</code></a> counterparts, they will

546

never return <code class="docutils literal">None</code>.

547

Besides, the <a class="reference internal" href="#io.BufferedIOBase.read" title="io.BufferedIOBase.read"><code class="xref py py-meth docutils literal">read()</code></a> method does not have a default

548

implementation that defers to <a class="reference internal" href="#io.BufferedIOBase.readinto" title="io.BufferedIOBase.readinto"><code class="xref py py-meth docutils literal">readinto()</code></a>.

549

A typical <a class="reference internal" href="#io.BufferedIOBase" title="io.BufferedIOBase"><code class="xref py py-class docutils literal">BufferedIOBase</code></a> implementation should not inherit from a

550

551

552

<a class="reference internal" href="#io.BufferedIOBase" title="io.BufferedIOBase"><code class="xref py py-class docutils literal">BufferedIOBase</code></a> provides or overrides these methods and attribute in

553

addition to those from <a class="reference internal" href="#io.IOBase" title="io.IOBase"><code class="xref py py-class docutils literal">IOBase</code></a>:

554

555

556

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<dd>The underlying raw stream (a <a class="reference internal" href="#io.RawIOBase" title="io.RawIOBase"><code class="xref py py-class docutils literal">RawIOBase</code></a> instance) that

558

559

560

</dd></dl>

561

562

563

564

<code class="descname">detach</code>()<a class="headerlink" href="#io.BufferedIOBase.detach" title="Permalink to this definition">¶</a></dt>

565

<dd>Separate the underlying raw stream from the buffer and return it.

566

After the raw stream has been detached, the buffer is in an unusable

567

state.

568

Some buffers, like <a class="reference internal" href="#io.BytesIO" title="io.BytesIO"><code class="xref py py-class docutils literal">BytesIO</code></a>, do not have the concept of a single

569

raw stream to return from this method. They raise

570

<a class="reference internal" href="#io.UnsupportedOperation" title="io.UnsupportedOperation"><code class="xref py py-exc docutils literal">UnsupportedOperation</code></a>.

571

572

New in version 3.1.

573

</div>

574

</dd></dl>

575

576

577

578

579

<dd>Read and return up to size bytes. If the argument is omitted, <code class="docutils literal">None</code>,

580

or negative, data is read and returned until EOF is reached. An empty

581

582

If the argument is positive, and the underlying raw stream is not

583

interactive, multiple raw reads may be issued to satisfy the byte count

584

(unless EOF is reached first). But for interactive raw streams, at most

585

one raw read will be issued, and a short result does not imply that EOF is

586

imminent.

587

A <a class="reference internal" href="exceptions.html#BlockingIOError" title="BlockingIOError"><code class="xref py py-exc docutils literal">BlockingIOError</code></a> is raised if the underlying raw stream is in

588

non blocking-mode, and has no data available at the moment.

589

</dd></dl>

590

591

592

593

594

<dd>Read and return up to size bytes, with at most one call to the

595

underlying raw stream’s <a class="reference internal" href="#io.RawIOBase.read" title="io.RawIOBase.read"><code class="xref py py-meth docutils literal">read()</code></a> (or

596

597

implementing your own buffering on top of a <a class="reference internal" href="#io.BufferedIOBase" title="io.BufferedIOBase"><code class="xref py py-class docutils literal">BufferedIOBase</code></a>

598

object.

599

</dd></dl>

600

601

602

603

<code class="descname">readinto</code>(b)<a class="headerlink" href="#io.BufferedIOBase.readinto" title="Permalink to this definition">¶</a></dt>

604

<dd>Read bytes into a pre-allocated, writable

605

<a class="reference internal" href="../glossary.html#term-bytes-like-object">bytes-like object</a> b and return the number of bytes read.

606

Like <a class="reference internal" href="#io.BufferedIOBase.read" title="io.BufferedIOBase.read"><code class="xref py py-meth docutils literal">read()</code></a>, multiple reads may be issued to the underlying raw

607

stream, unless the latter is interactive.

608

609

blocking-mode, and has no data available at the moment.

610

</dd></dl>

611

612

613

614

<code class="descname">readinto1</code>(b)<a class="headerlink" href="#io.BufferedIOBase.readinto1" title="Permalink to this definition">¶</a></dt>

615

<dd>Read bytes into a pre-allocated, writable

616

<a class="reference internal" href="../glossary.html#term-bytes-like-object">bytes-like object</a> b, using at most one call to

617

the underlying raw stream’s <a class="reference internal" href="#io.RawIOBase.read" title="io.RawIOBase.read"><code class="xref py py-meth docutils literal">read()</code></a> (or

618

619

620

blocking-mode, and has no data available at the moment.

621

622

New in version 3.5.

623

</div>

624

</dd></dl>

625

626

627

628

<code class="descname">write</code>(b)<a class="headerlink" href="#io.BufferedIOBase.write" title="Permalink to this definition">¶</a></dt>

629

<dd>Write the given <a class="reference internal" href="../glossary.html#term-bytes-like-object">bytes-like object</a>, b, and return the number

630

of bytes written (always equal to the length of b in bytes, since if

631

the write fails an <a class="reference internal" href="exceptions.html#OSError" title="OSError"><code class="xref py py-exc docutils literal">OSError</code></a> will be raised). Depending on the

632

actual implementation, these bytes may be readily written to the

633

underlying stream, or held in a buffer for performance and latency

634

reasons.

635

When in non-blocking mode, a <a class="reference internal" href="exceptions.html#BlockingIOError" title="BlockingIOError"><code class="xref py py-exc docutils literal">BlockingIOError</code></a> is raised if the

636

data needed to be written to the raw stream but it couldn’t accept

637

all the data without blocking.

638

The caller may release or mutate b after this method returns,

639

so the implementation should only access b during the method call.

640

</dd></dl>

641

642

</dd></dl>

643

644

</div>

645

646

647

648

649

class <code class="descclassname">io.</code><code class="descname">FileIO</code>(name, mode='r', closefd=True, opener=None)<a class="headerlink" href="#io.FileIO" title="Permalink to this definition">¶</a></dt>

650

<dd><a class="reference internal" href="#io.FileIO" title="io.FileIO"><code class="xref py py-class docutils literal">FileIO</code></a> represents an OS-level file containing bytes data.

651

It implements the <a class="reference internal" href="#io.RawIOBase" title="io.RawIOBase"><code class="xref py py-class docutils literal">RawIOBase</code></a> interface (and therefore the

652

<a class="reference internal" href="#io.IOBase" title="io.IOBase"><code class="xref py py-class docutils literal">IOBase</code></a> interface, too).

653

The name can be one of two things:

654

655

<li>a character string or <a class="reference internal" href="functions.html#bytes" title="bytes"><code class="xref py py-class docutils literal">bytes</code></a> object representing the path to the

656

file which will be opened. In this case closefd must be <code class="docutils literal">True</code> (the default)

657

otherwise an error will be raised.</li>

658

<li>an integer representing the number of an existing OS-level file descriptor

659

to which the resulting <a class="reference internal" href="#io.FileIO" title="io.FileIO"><code class="xref py py-class docutils literal">FileIO</code></a> object will give access. When the

660

FileIO object is closed this fd will be closed as well, unless closefd

661

is set to <code class="docutils literal">False</code>.</li>

662

</ul>

663

The mode can be <code class="docutils literal">'r'</code>, <code class="docutils literal">'w'</code>, <code class="docutils literal">'x'</code> or <code class="docutils literal">'a'</code> for reading

664

(default), writing, exclusive creation or appending. The file will be

665

created if it doesn’t exist when opened for writing or appending; it will be

666

truncated when opened for writing. <a class="reference internal" href="exceptions.html#FileExistsError" title="FileExistsError"><code class="xref py py-exc docutils literal">FileExistsError</code></a> will be raised if

667

it already exists when opened for creating. Opening a file for creating

668

implies writing, so this mode behaves in a similar way to <code class="docutils literal">'w'</code>. Add a

669

<code class="docutils literal">'+'</code> to the mode to allow simultaneous reading and writing.

670

The <code class="xref py py-meth docutils literal">read()</code> (when called with a positive argument), <code class="xref py py-meth docutils literal">readinto()</code>

671

and <code class="xref py py-meth docutils literal">write()</code> methods on this class will only make one system call.

672

A custom opener can be used by passing a callable as opener. The underlying

673

file descriptor for the file object is then obtained by calling opener with

674

(name, flags). opener must return an open file descriptor (passing

675

<a class="reference internal" href="os.html#os.open" title="os.open"><code class="xref py py-mod docutils literal">os.open</code></a> as opener results in functionality similar to passing

676

<code class="docutils literal">None</code>).

677

The newly created file is <a class="reference internal" href="os.html#fd-inheritance">non-inheritable</a>.

678

See the <a class="reference internal" href="functions.html#open" title="open"><code class="xref py py-func docutils literal">open()</code></a> built-in function for examples on using the opener

679

parameter.

680

681

Changed in version 3.3: The opener parameter was added.

682

The <code class="docutils literal">'x'</code> mode was added.

683

</div>

684

685

Changed in version 3.4: The file is now non-inheritable.

686

</div>

687

688

<a class="reference internal" href="#io.RawIOBase" title="io.RawIOBase"><code class="xref py py-class docutils literal">RawIOBase</code></a>, <a class="reference internal" href="#io.FileIO" title="io.FileIO"><code class="xref py py-class docutils literal">FileIO</code></a> provides the following data

689

attributes:

690

691

692

693

<dd>The mode as given in the constructor.

694

</dd></dl>

695

696

697

698

699

<dd>The file name. This is the file descriptor of the file when no name is

700

given in the constructor.

701

</dd></dl>

702

703

</dd></dl>

704

705

</div>

706

707

<h3>16.2.3.3. Buffered Streams<a class="headerlink" href="#buffered-streams" title="Permalink to this headline">¶</a></h3>

708

Buffered I/O streams provide a higher-level interface to an I/O device

709

than raw I/O does.

710

711

712

class <code class="descclassname">io.</code><code class="descname">BytesIO</code>([initial_bytes])<a class="headerlink" href="#io.BytesIO" title="Permalink to this definition">¶</a></dt>

713

<dd>A stream implementation using an in-memory bytes buffer. It inherits

714

715

<a class="reference internal" href="#io.IOBase.close" title="io.IOBase.close"><code class="xref py py-meth docutils literal">close()</code></a> method is called.

716

The optional argument initial_bytes is a <a class="reference internal" href="../glossary.html#term-bytes-like-object">bytes-like object</a> that

717

contains initial data.

718

<a class="reference internal" href="#io.BytesIO" title="io.BytesIO"><code class="xref py py-class docutils literal">BytesIO</code></a> provides or overrides these methods in addition to those

719

from <a class="reference internal" href="#io.BufferedIOBase" title="io.BufferedIOBase"><code class="xref py py-class docutils literal">BufferedIOBase</code></a> and <a class="reference internal" href="#io.IOBase" title="io.IOBase"><code class="xref py py-class docutils literal">IOBase</code></a>:

720

721

722

<code class="descname">getbuffer</code>()<a class="headerlink" href="#io.BytesIO.getbuffer" title="Permalink to this definition">¶</a></dt>

723

<dd>Return a readable and writable view over the contents of the buffer

724

without copying them. Also, mutating the view will transparently

725

update the contents of the buffer:

726

<div class="highlight-python3"><div class="highlight"><pre>>>> b = io.BytesIO(b"abcdef")

727

>>> view = b.getbuffer()

728

>>> view[2:4] = b"56"

729

>>> b.getvalue()

730

b'ab56ef'

731

</pre></div>

732

</div>

733

734

Note

735

As long as the view exists, the <a class="reference internal" href="#io.BytesIO" title="io.BytesIO"><code class="xref py py-class docutils literal">BytesIO</code></a> object cannot be

736

resized or closed.

737

</div>

738

739

New in version 3.2.

740

</div>

741

</dd></dl>

742

743

744

745

<code class="descname">getvalue</code>()<a class="headerlink" href="#io.BytesIO.getvalue" title="Permalink to this definition">¶</a></dt>

746

<dd>Return <a class="reference internal" href="functions.html#bytes" title="bytes"><code class="xref py py-class docutils literal">bytes</code></a> containing the entire contents of the buffer.

747

</dd></dl>

748

749

750

751

752

<dd>In <a class="reference internal" href="#io.BytesIO" title="io.BytesIO"><code class="xref py py-class docutils literal">BytesIO</code></a>, this is the same as <code class="xref py py-meth docutils literal">read()</code>.

753

</dd></dl>

754

755

756

757

<code class="descname">readinto1</code>()<a class="headerlink" href="#io.BytesIO.readinto1" title="Permalink to this definition">¶</a></dt>

758

759

760

New in version 3.5.

761

</div>

762

</dd></dl>

763

764

</dd></dl>

765

766

767

768

class <code class="descclassname">io.</code><code class="descname">BufferedReader</code>(raw, buffer_size=DEFAULT_BUFFER_SIZE)<a class="headerlink" href="#io.BufferedReader" title="Permalink to this definition">¶</a></dt>

769

<dd>A buffer providing higher-level access to a readable, sequential

770

<a class="reference internal" href="#io.RawIOBase" title="io.RawIOBase"><code class="xref py py-class docutils literal">RawIOBase</code></a> object. It inherits <a class="reference internal" href="#io.BufferedIOBase" title="io.BufferedIOBase"><code class="xref py py-class docutils literal">BufferedIOBase</code></a>.

771

When reading data from this object, a larger amount of data may be

772

requested from the underlying raw stream, and kept in an internal buffer.

773

The buffered data can then be returned directly on subsequent reads.

774

The constructor creates a <a class="reference internal" href="#io.BufferedReader" title="io.BufferedReader"><code class="xref py py-class docutils literal">BufferedReader</code></a> for the given readable

775

raw stream and buffer_size. If buffer_size is omitted,

776

<a class="reference internal" href="#io.DEFAULT_BUFFER_SIZE" title="io.DEFAULT_BUFFER_SIZE"><code class="xref py py-data docutils literal">DEFAULT_BUFFER_SIZE</code></a> is used.

777

<a class="reference internal" href="#io.BufferedReader" title="io.BufferedReader"><code class="xref py py-class docutils literal">BufferedReader</code></a> provides or overrides these methods in addition to

778

those from <a class="reference internal" href="#io.BufferedIOBase" title="io.BufferedIOBase"><code class="xref py py-class docutils literal">BufferedIOBase</code></a> and <a class="reference internal" href="#io.IOBase" title="io.IOBase"><code class="xref py py-class docutils literal">IOBase</code></a>:

779

780

781

782

<dd>Return bytes from the stream without advancing the position. At most one

783

single read on the raw stream is done to satisfy the call. The number of

784

bytes returned may be less or more than requested.

785

</dd></dl>

786

787

788

789

790

<dd>Read and return size bytes, or if size is not given or negative, until

791

EOF or if the read call would block in non-blocking mode.

792

</dd></dl>

793

794

795

796

797

<dd>Read and return up to size bytes with only one call on the raw stream.

798

If at least one byte is buffered, only buffered bytes are returned.

799

Otherwise, one raw stream read call is made.

800

</dd></dl>

801

802

</dd></dl>

803

804

805

806

class <code class="descclassname">io.</code><code class="descname">BufferedWriter</code>(raw, buffer_size=DEFAULT_BUFFER_SIZE)<a class="headerlink" href="#io.BufferedWriter" title="Permalink to this definition">¶</a></dt>

807

<dd>A buffer providing higher-level access to a writeable, sequential

808

<a class="reference internal" href="#io.RawIOBase" title="io.RawIOBase"><code class="xref py py-class docutils literal">RawIOBase</code></a> object. It inherits <a class="reference internal" href="#io.BufferedIOBase" title="io.BufferedIOBase"><code class="xref py py-class docutils literal">BufferedIOBase</code></a>.

809

When writing to this object, data is normally placed into an internal

810

buffer. The buffer will be written out to the underlying <a class="reference internal" href="#io.RawIOBase" title="io.RawIOBase"><code class="xref py py-class docutils literal">RawIOBase</code></a>

811

object under various conditions, including:

812

813

<li>when the buffer gets too small for all pending data;</li>

814

<li>when <a class="reference internal" href="#io.BufferedWriter.flush" title="io.BufferedWriter.flush"><code class="xref py py-meth docutils literal">flush()</code></a> is called;</li>

815

<li>when a <code class="xref py py-meth docutils literal">seek()</code> is requested (for <a class="reference internal" href="#io.BufferedRandom" title="io.BufferedRandom"><code class="xref py py-class docutils literal">BufferedRandom</code></a> objects);</li>

816

<li>when the <a class="reference internal" href="#io.BufferedWriter" title="io.BufferedWriter"><code class="xref py py-class docutils literal">BufferedWriter</code></a> object is closed or destroyed.</li>

817

</ul>

818

The constructor creates a <a class="reference internal" href="#io.BufferedWriter" title="io.BufferedWriter"><code class="xref py py-class docutils literal">BufferedWriter</code></a> for the given writeable

819

raw stream. If the buffer_size is not given, it defaults to

820

<a class="reference internal" href="#io.DEFAULT_BUFFER_SIZE" title="io.DEFAULT_BUFFER_SIZE"><code class="xref py py-data docutils literal">DEFAULT_BUFFER_SIZE</code></a>.

821

<a class="reference internal" href="#io.BufferedWriter" title="io.BufferedWriter"><code class="xref py py-class docutils literal">BufferedWriter</code></a> provides or overrides these methods in addition to

822

823

824

825

<code class="descname">flush</code>()<a class="headerlink" href="#io.BufferedWriter.flush" title="Permalink to this definition">¶</a></dt>

826

<dd>Force bytes held in the buffer into the raw stream. A

827

<a class="reference internal" href="exceptions.html#BlockingIOError" title="BlockingIOError"><code class="xref py py-exc docutils literal">BlockingIOError</code></a> should be raised if the raw stream blocks.

828

</dd></dl>

829

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831

832

<code class="descname">write</code>(b)<a class="headerlink" href="#io.BufferedWriter.write" title="Permalink to this definition">¶</a></dt>

833

<dd>Write the <a class="reference internal" href="../glossary.html#term-bytes-like-object">bytes-like object</a>, b, and return the

834

number of bytes written. When in non-blocking mode, a

835

836

the raw stream blocks.

837

</dd></dl>

838

839

</dd></dl>

840

841

842

843

class <code class="descclassname">io.</code><code class="descname">BufferedRandom</code>(raw, buffer_size=DEFAULT_BUFFER_SIZE)<a class="headerlink" href="#io.BufferedRandom" title="Permalink to this definition">¶</a></dt>

844

<dd>A buffered interface to random access streams. It inherits

845

<a class="reference internal" href="#io.BufferedReader" title="io.BufferedReader"><code class="xref py py-class docutils literal">BufferedReader</code></a> and <a class="reference internal" href="#io.BufferedWriter" title="io.BufferedWriter"><code class="xref py py-class docutils literal">BufferedWriter</code></a>, and further supports

846

<code class="xref py py-meth docutils literal">seek()</code> and <code class="xref py py-meth docutils literal">tell()</code> functionality.

847

The constructor creates a reader and writer for a seekable raw stream, given

848

in the first argument. If the buffer_size is omitted it defaults to

849

<a class="reference internal" href="#io.DEFAULT_BUFFER_SIZE" title="io.DEFAULT_BUFFER_SIZE"><code class="xref py py-data docutils literal">DEFAULT_BUFFER_SIZE</code></a>.

850

<a class="reference internal" href="#io.BufferedRandom" title="io.BufferedRandom"><code class="xref py py-class docutils literal">BufferedRandom</code></a> is capable of anything <a class="reference internal" href="#io.BufferedReader" title="io.BufferedReader"><code class="xref py py-class docutils literal">BufferedReader</code></a> or

851

<a class="reference internal" href="#io.BufferedWriter" title="io.BufferedWriter"><code class="xref py py-class docutils literal">BufferedWriter</code></a> can do.

852

</dd></dl>

853

854

855

856

class <code class="descclassname">io.</code><code class="descname">BufferedRWPair</code>(reader, writer, buffer_size=DEFAULT_BUFFER_SIZE)<a class="headerlink" href="#io.BufferedRWPair" title="Permalink to this definition">¶</a></dt>

857

<dd>A buffered I/O object combining two unidirectional <a class="reference internal" href="#io.RawIOBase" title="io.RawIOBase"><code class="xref py py-class docutils literal">RawIOBase</code></a>

858

objects – one readable, the other writeable – into a single bidirectional

859

endpoint. It inherits <a class="reference internal" href="#io.BufferedIOBase" title="io.BufferedIOBase"><code class="xref py py-class docutils literal">BufferedIOBase</code></a>.

860

reader and writer are <a class="reference internal" href="#io.RawIOBase" title="io.RawIOBase"><code class="xref py py-class docutils literal">RawIOBase</code></a> objects that are readable and

861

writeable respectively. If the buffer_size is omitted it defaults to

862

<a class="reference internal" href="#io.DEFAULT_BUFFER_SIZE" title="io.DEFAULT_BUFFER_SIZE"><code class="xref py py-data docutils literal">DEFAULT_BUFFER_SIZE</code></a>.

863

<a class="reference internal" href="#io.BufferedRWPair" title="io.BufferedRWPair"><code class="xref py py-class docutils literal">BufferedRWPair</code></a> implements all of <a class="reference internal" href="#io.BufferedIOBase" title="io.BufferedIOBase"><code class="xref py py-class docutils literal">BufferedIOBase</code></a>‘s methods

864

except for <a class="reference internal" href="#io.BufferedIOBase.detach" title="io.BufferedIOBase.detach"><code class="xref py py-meth docutils literal">detach()</code></a>, which raises

865

866

867

Warning

868

<a class="reference internal" href="#io.BufferedRWPair" title="io.BufferedRWPair"><code class="xref py py-class docutils literal">BufferedRWPair</code></a> does not attempt to synchronize accesses to

869

its underlying raw streams. You should not pass it the same object

870

as reader and writer; use <a class="reference internal" href="#io.BufferedRandom" title="io.BufferedRandom"><code class="xref py py-class docutils literal">BufferedRandom</code></a> instead.

871

</div>

872

</dd></dl>

873

874

</div>

875

876

877

878

879

class <code class="descclassname">io.</code><code class="descname">TextIOBase</code><a class="headerlink" href="#io.TextIOBase" title="Permalink to this definition">¶</a></dt>

880

<dd>Base class for text streams. This class provides a character and line based

881

interface to stream I/O. There is no <code class="xref py py-meth docutils literal">readinto()</code> method because

882

Python’s character strings are immutable. It inherits <a class="reference internal" href="#io.IOBase" title="io.IOBase"><code class="xref py py-class docutils literal">IOBase</code></a>.

883

There is no public constructor.

884

<a class="reference internal" href="#io.TextIOBase" title="io.TextIOBase"><code class="xref py py-class docutils literal">TextIOBase</code></a> provides or overrides these data attributes and

885

methods in addition to those from <a class="reference internal" href="#io.IOBase" title="io.IOBase"><code class="xref py py-class docutils literal">IOBase</code></a>:

886

887

888

<code class="descname">encoding</code><a class="headerlink" href="#io.TextIOBase.encoding" title="Permalink to this definition">¶</a></dt>

889

<dd>The name of the encoding used to decode the stream’s bytes into

890

strings, and to encode strings into bytes.

891

</dd></dl>

892

893

894

895

<code class="descname">errors</code><a class="headerlink" href="#io.TextIOBase.errors" title="Permalink to this definition">¶</a></dt>

896

<dd>The error setting of the decoder or encoder.

897

</dd></dl>

898

899

900

901

<code class="descname">newlines</code><a class="headerlink" href="#io.TextIOBase.newlines" title="Permalink to this definition">¶</a></dt>

902

<dd>A string, a tuple of strings, or <code class="docutils literal">None</code>, indicating the newlines

903

translated so far. Depending on the implementation and the initial

904

constructor flags, this may not be available.

905

</dd></dl>

906

907

908

909

<code class="descname">buffer</code><a class="headerlink" href="#io.TextIOBase.buffer" title="Permalink to this definition">¶</a></dt>

910

<dd>The underlying binary buffer (a <a class="reference internal" href="#io.BufferedIOBase" title="io.BufferedIOBase"><code class="xref py py-class docutils literal">BufferedIOBase</code></a> instance) that

911

<a class="reference internal" href="#io.TextIOBase" title="io.TextIOBase"><code class="xref py py-class docutils literal">TextIOBase</code></a> deals with. This is not part of the

912

913

</dd></dl>

914

915

916

917

<code class="descname">detach</code>()<a class="headerlink" href="#io.TextIOBase.detach" title="Permalink to this definition">¶</a></dt>

918

<dd>Separate the underlying binary buffer from the <a class="reference internal" href="#io.TextIOBase" title="io.TextIOBase"><code class="xref py py-class docutils literal">TextIOBase</code></a> and

919

return it.

920

After the underlying buffer has been detached, the <a class="reference internal" href="#io.TextIOBase" title="io.TextIOBase"><code class="xref py py-class docutils literal">TextIOBase</code></a> is

921

in an unusable state.

922

Some <a class="reference internal" href="#io.TextIOBase" title="io.TextIOBase"><code class="xref py py-class docutils literal">TextIOBase</code></a> implementations, like <a class="reference internal" href="#io.StringIO" title="io.StringIO"><code class="xref py py-class docutils literal">StringIO</code></a>, may not

923

have the concept of an underlying buffer and calling this method will

924

raise <a class="reference internal" href="#io.UnsupportedOperation" title="io.UnsupportedOperation"><code class="xref py py-exc docutils literal">UnsupportedOperation</code></a>.

925

926

New in version 3.1.

927

</div>

928

</dd></dl>

929

930

931

932

933

<dd>Read and return at most size characters from the stream as a single

934

<a class="reference internal" href="stdtypes.html#str" title="str"><code class="xref py py-class docutils literal">str</code></a>. If size is negative or <code class="docutils literal">None</code>, reads until EOF.

935

</dd></dl>

936

937

938

939

<code class="descname">readline</code>(size=-1)<a class="headerlink" href="#io.TextIOBase.readline" title="Permalink to this definition">¶</a></dt>

940

<dd>Read until newline or EOF and return a single <code class="docutils literal">str</code>. If the stream is

941

already at EOF, an empty string is returned.

942

If size is specified, at most size characters will be read.

943

</dd></dl>

944

945

946

947

<code class="descname">seek</code>(offset[, whence])<a class="headerlink" href="#io.TextIOBase.seek" title="Permalink to this definition">¶</a></dt>

948

<dd>Change the stream position to the given offset. Behaviour depends on

949

the whence parameter. The default value for whence is

950

<code class="xref py py-data docutils literal">SEEK_SET</code>.

951

952

<li><code class="xref py py-data docutils literal">SEEK_SET</code> or <code class="docutils literal">0</code>: seek from the start of the stream

953

(the default); offset must either be a number returned by

954

<a class="reference internal" href="#io.TextIOBase.tell" title="io.TextIOBase.tell"><code class="xref py py-meth docutils literal">TextIOBase.tell()</code></a>, or zero. Any other offset value

955

produces undefined behaviour.</li>

956

<li><code class="xref py py-data docutils literal">SEEK_CUR</code> or <code class="docutils literal">1</code>: “seek” to the current position;

957

offset must be zero, which is a no-operation (all other values

958

are unsupported).</li>

959

<li><code class="xref py py-data docutils literal">SEEK_END</code> or <code class="docutils literal">2</code>: seek to the end of the stream;

960

offset must be zero (all other values are unsupported).</li>

961

</ul>

962

Return the new absolute position as an opaque number.

963

964

New in version 3.1: The <code class="docutils literal">SEEK_*</code> constants.

965

</div>

966

</dd></dl>

967

968

969

970

971

<dd>Return the current stream position as an opaque number. The number

972

does not usually represent a number of bytes in the underlying

973

binary storage.

974

</dd></dl>

975

976

977

978

<code class="descname">write</code>(s)<a class="headerlink" href="#io.TextIOBase.write" title="Permalink to this definition">¶</a></dt>

979

<dd>Write the string s to the stream and return the number of characters

980

written.

981

</dd></dl>

982

983

</dd></dl>

984

985

986

987

class <code class="descclassname">io.</code><code class="descname">TextIOWrapper</code>(buffer, encoding=None, errors=None, newline=None, line_buffering=False, write_through=False)<a class="headerlink" href="#io.TextIOWrapper" title="Permalink to this definition">¶</a></dt>

988

<dd>A buffered text stream over a <a class="reference internal" href="#io.BufferedIOBase" title="io.BufferedIOBase"><code class="xref py py-class docutils literal">BufferedIOBase</code></a> binary stream.

989

It inherits <a class="reference internal" href="#io.TextIOBase" title="io.TextIOBase"><code class="xref py py-class docutils literal">TextIOBase</code></a>.

990

encoding gives the name of the encoding that the stream will be decoded or

991

encoded with. It defaults to

992

<a class="reference internal" href="locale.html#locale.getpreferredencoding" title="locale.getpreferredencoding"><code class="xref py py-func docutils literal">locale.getpreferredencoding(False)</code></a>.

993

errors is an optional string that specifies how encoding and decoding

994

errors are to be handled. Pass <code class="docutils literal">'strict'</code> to raise a <a class="reference internal" href="exceptions.html#ValueError" title="ValueError"><code class="xref py py-exc docutils literal">ValueError</code></a>

995

exception if there is an encoding error (the default of <code class="docutils literal">None</code> has the same

996

effect), or pass <code class="docutils literal">'ignore'</code> to ignore errors. (Note that ignoring encoding

997

errors can lead to data loss.) <code class="docutils literal">'replace'</code> causes a replacement marker

998

(such as <code class="docutils literal">'?'</code>) to be inserted where there is malformed data.

999

<code class="docutils literal">'backslashreplace'</code> causes malformed data to be replaced by a

1000

backslashed escape sequence. When writing, <code class="docutils literal">'xmlcharrefreplace'</code>

1001

(replace with the appropriate XML character reference) or <code class="docutils literal">'namereplace'</code>

1002

(replace with <code class="docutils literal">\N{...}</code> escape sequences) can be used. Any other error

1003

handling name that has been registered with

1004

<a class="reference internal" href="codecs.html#codecs.register_error" title="codecs.register_error"><code class="xref py py-func docutils literal">codecs.register_error()</code></a> is also valid.

1005

newline controls how line endings are handled. It can be <code class="docutils literal">None</code>,

1006

<code class="docutils literal">''</code>, <code class="docutils literal">'\n'</code>, <code class="docutils literal">'\r'</code>, and <code class="docutils literal">'\r\n'</code>. It works as follows:

1007

1008

<li>When reading input from the stream, if newline is <code class="docutils literal">None</code>,

1009

<a class="reference internal" href="../glossary.html#term-universal-newlines">universal newlines</a> mode is enabled. Lines in the input can end in

1010

<code class="docutils literal">'\n'</code>, <code class="docutils literal">'\r'</code>, or <code class="docutils literal">'\r\n'</code>, and these are translated into <code class="docutils literal">'\n'</code>

1011

before being returned to the caller. If it is <code class="docutils literal">''</code>, universal newlines

1012

mode is enabled, but line endings are returned to the caller untranslated.

1013

If it has any of the other legal values, input lines are only terminated

1014

by the given string, and the line ending is returned to the caller

1015

untranslated.</li>

1016

<li>When writing output to the stream, if newline is <code class="docutils literal">None</code>, any <code class="docutils literal">'\n'</code>

1017

characters written are translated to the system default line separator,

1018

<a class="reference internal" href="os.html#os.linesep" title="os.linesep"><code class="xref py py-data docutils literal">os.linesep</code></a>. If newline is <code class="docutils literal">''</code> or <code class="docutils literal">'\n'</code>, no translation

1019

takes place. If newline is any of the other legal values, any <code class="docutils literal">'\n'</code>

1020

characters written are translated to the given string.</li>

1021

</ul>

1022

If line_buffering is <code class="docutils literal">True</code>, <code class="xref py py-meth docutils literal">flush()</code> is implied when a call to

1023

write contains a newline character.

1024

If write_through is <code class="docutils literal">True</code>, calls to <code class="xref py py-meth docutils literal">write()</code> are guaranteed

1025

not to be buffered: any data written on the <a class="reference internal" href="#io.TextIOWrapper" title="io.TextIOWrapper"><code class="xref py py-class docutils literal">TextIOWrapper</code></a>

1026

object is immediately handled to its underlying binary buffer.

1027

1028

Changed in version 3.3: The write_through argument has been added.

1029

</div>

1030

1031

Changed in version 3.3: The default encoding is now <code class="docutils literal">locale.getpreferredencoding(False)</code>

1032

instead of <code class="docutils literal">locale.getpreferredencoding()</code>. Don’t change temporary the

1033

locale encoding using <a class="reference internal" href="locale.html#locale.setlocale" title="locale.setlocale"><code class="xref py py-func docutils literal">locale.setlocale()</code></a>, use the current locale

1034

encoding instead of the user preferred encoding.

1035

</div>

1036

<a class="reference internal" href="#io.TextIOWrapper" title="io.TextIOWrapper"><code class="xref py py-class docutils literal">TextIOWrapper</code></a> provides one attribute in addition to those of

1037

<a class="reference internal" href="#io.TextIOBase" title="io.TextIOBase"><code class="xref py py-class docutils literal">TextIOBase</code></a> and its parents:

1038

1039

1040

<code class="descname">line_buffering</code><a class="headerlink" href="#io.TextIOWrapper.line_buffering" title="Permalink to this definition">¶</a></dt>

1041

<dd>Whether line buffering is enabled.

1042

</dd></dl>

1043

1044

</dd></dl>

1045

1046

1047

1048

class <code class="descclassname">io.</code><code class="descname">StringIO</code>(initial_value='', newline='\n')<a class="headerlink" href="#io.StringIO" title="Permalink to this definition">¶</a></dt>

1049

<dd>An in-memory stream for text I/O. The text buffer is discarded when the

1050

<a class="reference internal" href="#io.IOBase.close" title="io.IOBase.close"><code class="xref py py-meth docutils literal">close()</code></a> method is called.

1051

The initial value of the buffer can be set by providing initial_value.

1052

If newline translation is enabled, newlines will be encoded as if by

1053

<a class="reference internal" href="#io.TextIOBase.write" title="io.TextIOBase.write"><code class="xref py py-meth docutils literal">write()</code></a>. The stream is positioned at the start of

1054

the buffer.

1055

The newline argument works like that of <a class="reference internal" href="#io.TextIOWrapper" title="io.TextIOWrapper"><code class="xref py py-class docutils literal">TextIOWrapper</code></a>.

1056

The default is to consider only <code class="docutils literal">\n</code> characters as ends of lines and

1057

to do no newline translation. If newline is set to <code class="docutils literal">None</code>,

1058

newlines are written as <code class="docutils literal">\n</code> on all platforms, but universal

1059

newline decoding is still performed when reading.

1060

<a class="reference internal" href="#io.StringIO" title="io.StringIO"><code class="xref py py-class docutils literal">StringIO</code></a> provides this method in addition to those from

1061

<a class="reference internal" href="#io.TextIOBase" title="io.TextIOBase"><code class="xref py py-class docutils literal">TextIOBase</code></a> and its parents:

1062

1063

1064

<code class="descname">getvalue</code>()<a class="headerlink" href="#io.StringIO.getvalue" title="Permalink to this definition">¶</a></dt>

1065

<dd>Return a <code class="docutils literal">str</code> containing the entire contents of the buffer.

1066

Newlines are decoded as if by <a class="reference internal" href="#io.TextIOBase.read" title="io.TextIOBase.read"><code class="xref py py-meth docutils literal">read()</code></a>, although

1067

the stream position is not changed.

1068

</dd></dl>

1069

1070

Example usage:

1071

<div class="highlight-python3"><div class="highlight"><pre>import io

1072

1073

output = io.StringIO()

1074

output.write('First line.\n')

1075

print('Second line.', file=output)

1076

1077

# Retrieve file contents -- this will be

1078

# 'First line.\nSecond line.\n'

1079

contents = output.getvalue()

1080

1081

# Close object and discard memory buffer --

1082

# .getvalue() will now raise an exception.

1083

output.close()

1084

</pre></div>

1085

</div>

1086

</dd></dl>

1087

1088

1089

1090

class <code class="descclassname">io.</code><code class="descname">IncrementalNewlineDecoder</code><a class="headerlink" href="#io.IncrementalNewlineDecoder" title="Permalink to this definition">¶</a></dt>

1091

<dd>A helper codec that decodes newlines for <a class="reference internal" href="../glossary.html#term-universal-newlines">universal newlines</a> mode.

1092

It inherits <a class="reference internal" href="codecs.html#codecs.IncrementalDecoder" title="codecs.IncrementalDecoder"><code class="xref py py-class docutils literal">codecs.IncrementalDecoder</code></a>.

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</dd></dl>

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</div>

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</div>

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<h2>16.2.4. Performance<a class="headerlink" href="#performance" title="Permalink to this headline">¶</a></h2>

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This section discusses the performance of the provided concrete I/O

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implementations.

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<h3>16.2.4.1. Binary I/O<a class="headerlink" href="#id2" title="Permalink to this headline">¶</a></h3>

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By reading and writing only large chunks of data even when the user asks for a

1104

single byte, buffered I/O hides any inefficiency in calling and executing the

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operating system’s unbuffered I/O routines. The gain depends on the OS and the

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kind of I/O which is performed. For example, on some modern OSes such as Linux,

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unbuffered disk I/O can be as fast as buffered I/O. The bottom line, however,

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is that buffered I/O offers predictable performance regardless of the platform

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and the backing device. Therefore, it is almost always preferable to use

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buffered I/O rather than unbuffered I/O for binary data.

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</div>

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Text I/O over a binary storage (such as a file) is significantly slower than

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binary I/O over the same storage, because it requires conversions between

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unicode and binary data using a character codec. This can become noticeable

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handling huge amounts of text data like large log files. Also,

1118

<code class="xref py py-meth docutils literal">TextIOWrapper.tell()</code> and <code class="xref py py-meth docutils literal">TextIOWrapper.seek()</code> are both quite slow

1119

due to the reconstruction algorithm used.

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exhibit similar speed to <a class="reference internal" href="#io.BytesIO" title="io.BytesIO"><code class="xref py py-class docutils literal">BytesIO</code></a>.

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</div>

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<h3>16.2.4.3. Multi-threading<a class="headerlink" href="#multi-threading" title="Permalink to this headline">¶</a></h3>

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<a class="reference internal" href="#io.FileIO" title="io.FileIO"><code class="xref py py-class docutils literal">FileIO</code></a> objects are thread-safe to the extent that the operating system

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calls (such as <code class="docutils literal">read(2)</code> under Unix) they wrap are thread-safe too.

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Binary buffered objects (instances of <a class="reference internal" href="#io.BufferedReader" title="io.BufferedReader"><code class="xref py py-class docutils literal">BufferedReader</code></a>,

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<a class="reference internal" href="#io.BufferedWriter" title="io.BufferedWriter"><code class="xref py py-class docutils literal">BufferedWriter</code></a>, <a class="reference internal" href="#io.BufferedRandom" title="io.BufferedRandom"><code class="xref py py-class docutils literal">BufferedRandom</code></a> and <a class="reference internal" href="#io.BufferedRWPair" title="io.BufferedRWPair"><code class="xref py py-class docutils literal">BufferedRWPair</code></a>)

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protect their internal structures using a lock; it is therefore safe to call

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them from multiple threads at once.

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</div>

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<h3>16.2.4.4. Reentrancy<a class="headerlink" href="#reentrancy" title="Permalink to this headline">¶</a></h3>

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are not reentrant. While reentrant calls will not happen in normal situations,

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they can arise from doing I/O in a <a class="reference internal" href="signal.html#module-signal" title="signal: Set handlers for asynchronous events."><code class="xref py py-mod docutils literal">signal</code></a> handler. If a thread tries to

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re-enter a buffered object which it is already accessing, a <a class="reference internal" href="exceptions.html#RuntimeError" title="RuntimeError"><code class="xref py py-exc docutils literal">RuntimeError</code></a>

1140

is raised. Note this doesn’t prohibit a different thread from entering the

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buffered object.

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The above implicitly extends to text files, since the <a class="reference internal" href="functions.html#open" title="open"><code class="xref py py-func docutils literal">open()</code></a> function

1143

will wrap a buffered object inside a <a class="reference internal" href="#io.TextIOWrapper" title="io.TextIOWrapper"><code class="xref py py-class docutils literal">TextIOWrapper</code></a>. This includes

1144

standard streams and therefore affects the built-in function <a class="reference internal" href="functions.html#print" title="print"><code class="xref py py-func docutils literal">print()</code></a> as

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well.

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</div>

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</div>

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</div>

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</div>

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</div>

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</div>

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<h3><a href="../contents.html">Table Of Contents</a></h3>

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<ul>

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<li><a class="reference internal" href="#">16.2. <code class="docutils literal">io</code> — Core tools for working with streams</a><ul>

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<li><a class="reference internal" href="#overview">16.2.1. Overview</a><ul>

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<li><a class="reference internal" href="#binary-i-o">16.2.1.2. Binary I/O</a></li>

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1163

</ul>

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</li>

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<li><a class="reference internal" href="#high-level-module-interface">16.2.2. High-level Module Interface</a><ul>

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<li><a class="reference internal" href="#in-memory-streams">16.2.2.1. In-memory streams</a></li>

1167

</ul>

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</li>

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<li><a class="reference internal" href="#class-hierarchy">16.2.3. Class hierarchy</a><ul>

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<li><a class="reference internal" href="#i-o-base-classes">16.2.3.1. I/O Base Classes</a></li>

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<li><a class="reference internal" href="#buffered-streams">16.2.3.3. Buffered Streams</a></li>

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1174

</ul>

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</li>

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<li><a class="reference internal" href="#performance">16.2.4. Performance</a><ul>

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<li><a class="reference internal" href="#id2">16.2.4.1. Binary I/O</a></li>

1178

1179

<li><a class="reference internal" href="#multi-threading">16.2.4.3. Multi-threading</a></li>

1180

<li><a class="reference internal" href="#reentrancy">16.2.4.4. Reentrancy</a></li>

1181

</ul>

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</li>

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</ul>

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</li>

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</ul>

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<h4>Previous topic</h4>

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<a href="os.html"

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title="previous chapter">16.1. <code class="docutils literal">os</code> — Miscellaneous operating system interfaces</a>

1190

<h4>Next topic</h4>

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<a href="time.html"

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title="next chapter">16.3. <code class="docutils literal">time</code> — Time access and conversions</a>

1193

1194

1195

1196

<li><a href="../bugs.html">Report a Bug</a></li>

1197

<li><a href="../_sources/library/io.txt"

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rel="nofollow">Show Source</a></li>

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</ul>

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