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<div class="section" id="repr-alternate-repr-implementation">
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<h1>8.19. <a class="reference internal" href="functions.html#repr" title="repr"><code class="xref py py-mod docutils literal"><span class="pre">repr</span></code></a> — Alternate <a class="reference internal" href="functions.html#repr" title="repr"><code class="xref py py-func docutils literal"><span class="pre">repr()</span></code></a> implementation<a class="headerlink" href="#repr-alternate-repr-implementation" title="Permalink to this headline">¶</a></h1>
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<div class="admonition note">
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<p class="first admonition-title">Note</p>
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<p class="last">The <a class="reference internal" href="functions.html#repr" title="repr"><code class="xref py py-mod docutils literal"><span class="pre">repr</span></code></a> module has been renamed to <code class="xref py py-mod docutils literal"><span class="pre">reprlib</span></code> in Python 3. The
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<a class="reference internal" href="../glossary.html#term-2to3"><span class="xref std std-term">2to3</span></a> tool will automatically adapt imports when converting your
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sources to Python 3.</p>
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<p><strong>Source code:</strong> <a class="reference external" href="https://hg.python.org/cpython/file/2.7/Lib/repr.py">Lib/repr.py</a></p>
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<hr class="docutils" />
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<p>The <a class="reference internal" href="functions.html#repr" title="repr"><code class="xref py py-mod docutils literal"><span class="pre">repr</span></code></a> module provides a means for producing object representations
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with limits on the size of the resulting strings. This is used in the Python
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debugger and may be useful in other contexts as well.</p>
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<p>This module provides a class, an instance, and a function:</p>
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<em class="property">class </em><code class="descclassname">repr.</code><code class="descname">Repr</code><a class="headerlink" href="#repr.Repr" title="Permalink to this definition">¶</a></dt>
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<dd><p>Class which provides formatting services useful in implementing functions
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similar to the built-in <a class="reference internal" href="functions.html#func-repr"><span>repr()</span></a>; size limits for different
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object types are added to avoid the generation of representations which are
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<code class="descclassname">repr.</code><code class="descname">aRepr</code><a class="headerlink" href="#repr.aRepr" title="Permalink to this definition">¶</a></dt>
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<dd><p>This is an instance of <a class="reference internal" href="#repr.Repr" title="repr.Repr"><code class="xref py py-class docutils literal"><span class="pre">Repr</span></code></a> which is used to provide the <a class="reference internal" href="#repr.repr" title="repr.repr"><code class="xref py py-func docutils literal"><span class="pre">repr()</span></code></a>
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function described below. Changing the attributes of this object will affect
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the size limits used by <a class="reference internal" href="#repr.repr" title="repr.repr"><code class="xref py py-func docutils literal"><span class="pre">repr()</span></code></a> and the Python debugger.</p>
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<dl class="function">
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<code class="descclassname">repr.</code><code class="descname">repr</code><span class="sig-paren">(</span><em>obj</em><span class="sig-paren">)</span><a class="headerlink" href="#repr.repr" title="Permalink to this definition">¶</a></dt>
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<dd><p>This is the <a class="reference internal" href="#repr.Repr.repr" title="repr.Repr.repr"><code class="xref py py-meth docutils literal"><span class="pre">repr()</span></code></a> method of <code class="docutils literal"><span class="pre">aRepr</span></code>. It returns a string
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similar to that returned by the built-in function of the same name, but with
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limits on most sizes.</p>
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<div class="section" id="repr-objects">
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<span id="id1"></span><h2>8.19.1. Repr Objects<a class="headerlink" href="#repr-objects" title="Permalink to this headline">¶</a></h2>
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<p><a class="reference internal" href="#repr.Repr" title="repr.Repr"><code class="xref py py-class docutils literal"><span class="pre">Repr</span></code></a> instances provide several attributes which can be used to provide
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size limits for the representations of different object types, and methods
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which format specific object types.</p>
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<dl class="attribute">
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<dt id="repr.Repr.maxlevel">
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<code class="descclassname">Repr.</code><code class="descname">maxlevel</code><a class="headerlink" href="#repr.Repr.maxlevel" title="Permalink to this definition">¶</a></dt>
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<dd><p>Depth limit on the creation of recursive representations. The default is <code class="docutils literal"><span class="pre">6</span></code>.</p>
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<dl class="attribute">
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<dt id="repr.Repr.maxdict">
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<code class="descclassname">Repr.</code><code class="descname">maxdict</code><a class="headerlink" href="#repr.Repr.maxdict" title="Permalink to this definition">¶</a></dt>
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<dt id="repr.Repr.maxlist">
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<code class="descclassname">Repr.</code><code class="descname">maxlist</code><a class="headerlink" href="#repr.Repr.maxlist" title="Permalink to this definition">¶</a></dt>
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<dt id="repr.Repr.maxtuple">
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<code class="descclassname">Repr.</code><code class="descname">maxtuple</code><a class="headerlink" href="#repr.Repr.maxtuple" title="Permalink to this definition">¶</a></dt>
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<dt id="repr.Repr.maxset">
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<code class="descclassname">Repr.</code><code class="descname">maxset</code><a class="headerlink" href="#repr.Repr.maxset" title="Permalink to this definition">¶</a></dt>
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<dt id="repr.Repr.maxfrozenset">
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<code class="descclassname">Repr.</code><code class="descname">maxfrozenset</code><a class="headerlink" href="#repr.Repr.maxfrozenset" title="Permalink to this definition">¶</a></dt>
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<dt id="repr.Repr.maxdeque">
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<code class="descclassname">Repr.</code><code class="descname">maxdeque</code><a class="headerlink" href="#repr.Repr.maxdeque" title="Permalink to this definition">¶</a></dt>
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<dt id="repr.Repr.maxarray">
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<code class="descclassname">Repr.</code><code class="descname">maxarray</code><a class="headerlink" href="#repr.Repr.maxarray" title="Permalink to this definition">¶</a></dt>
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<dd><p>Limits on the number of entries represented for the named object type. The
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default is <code class="docutils literal"><span class="pre">4</span></code> for <a class="reference internal" href="#repr.Repr.maxdict" title="repr.Repr.maxdict"><code class="xref py py-attr docutils literal"><span class="pre">maxdict</span></code></a>, <code class="docutils literal"><span class="pre">5</span></code> for <a class="reference internal" href="#repr.Repr.maxarray" title="repr.Repr.maxarray"><code class="xref py py-attr docutils literal"><span class="pre">maxarray</span></code></a>, and <code class="docutils literal"><span class="pre">6</span></code> for
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<div class="versionadded">
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<p><span class="versionmodified">New in version 2.4: </span><a class="reference internal" href="#repr.Repr.maxset" title="repr.Repr.maxset"><code class="xref py py-attr docutils literal"><span class="pre">maxset</span></code></a>, <a class="reference internal" href="#repr.Repr.maxfrozenset" title="repr.Repr.maxfrozenset"><code class="xref py py-attr docutils literal"><span class="pre">maxfrozenset</span></code></a>, and <a class="reference internal" href="stdtypes.html#set" title="set"><code class="xref py py-attr docutils literal"><span class="pre">set</span></code></a>.</p>
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<dl class="attribute">
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<dt id="repr.Repr.maxlong">
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<code class="descclassname">Repr.</code><code class="descname">maxlong</code><a class="headerlink" href="#repr.Repr.maxlong" title="Permalink to this definition">¶</a></dt>
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<dd><p>Maximum number of characters in the representation for a long integer. Digits
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are dropped from the middle. The default is <code class="docutils literal"><span class="pre">40</span></code>.</p>
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<dl class="attribute">
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<dt id="repr.Repr.maxstring">
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<code class="descclassname">Repr.</code><code class="descname">maxstring</code><a class="headerlink" href="#repr.Repr.maxstring" title="Permalink to this definition">¶</a></dt>
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<dd><p>Limit on the number of characters in the representation of the string. Note
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that the “normal” representation of the string is used as the character source:
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if escape sequences are needed in the representation, these may be mangled when
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the representation is shortened. The default is <code class="docutils literal"><span class="pre">30</span></code>.</p>
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<dl class="attribute">
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<dt id="repr.Repr.maxother">
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<code class="descclassname">Repr.</code><code class="descname">maxother</code><a class="headerlink" href="#repr.Repr.maxother" title="Permalink to this definition">¶</a></dt>
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<dd><p>This limit is used to control the size of object types for which no specific
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formatting method is available on the <a class="reference internal" href="#repr.Repr" title="repr.Repr"><code class="xref py py-class docutils literal"><span class="pre">Repr</span></code></a> object. It is applied in a
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similar manner as <a class="reference internal" href="#repr.Repr.maxstring" title="repr.Repr.maxstring"><code class="xref py py-attr docutils literal"><span class="pre">maxstring</span></code></a>. The default is <code class="docutils literal"><span class="pre">20</span></code>.</p>
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<dt id="repr.Repr.repr">
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<code class="descclassname">Repr.</code><code class="descname">repr</code><span class="sig-paren">(</span><em>obj</em><span class="sig-paren">)</span><a class="headerlink" href="#repr.Repr.repr" title="Permalink to this definition">¶</a></dt>
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<dd><p>The equivalent to the built-in <a class="reference internal" href="functions.html#func-repr"><span>repr()</span></a> that uses the
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formatting imposed by the instance.</p>
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<dt id="repr.Repr.repr1">
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<code class="descclassname">Repr.</code><code class="descname">repr1</code><span class="sig-paren">(</span><em>obj</em>, <em>level</em><span class="sig-paren">)</span><a class="headerlink" href="#repr.Repr.repr1" title="Permalink to this definition">¶</a></dt>
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<dd><p>Recursive implementation used by <a class="reference internal" href="#repr.Repr.repr" title="repr.Repr.repr"><code class="xref py py-meth docutils literal"><span class="pre">repr()</span></code></a>. This uses the type of <em>obj</em> to
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determine which formatting method to call, passing it <em>obj</em> and <em>level</em>. The
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type-specific methods should call <a class="reference internal" href="#repr.Repr.repr1" title="repr.Repr.repr1"><code class="xref py py-meth docutils literal"><span class="pre">repr1()</span></code></a> to perform recursive formatting,
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with <code class="docutils literal"><span class="pre">level</span> <span class="pre">-</span> <span class="pre">1</span></code> for the value of <em>level</em> in the recursive call.</p>
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<code class="descclassname">Repr.</code><code class="descname">repr_TYPE</code><span class="sig-paren">(</span><em>obj</em>, <em>level</em><span class="sig-paren">)</span></dt>
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<dd><p>Formatting methods for specific types are implemented as methods with a name
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based on the type name. In the method name, <strong>TYPE</strong> is replaced by
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<code class="docutils literal"><span class="pre">string.join(string.split(type(obj).__name__,</span> <span class="pre">'_'))</span></code>. Dispatch to these
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methods is handled by <a class="reference internal" href="#repr.Repr.repr1" title="repr.Repr.repr1"><code class="xref py py-meth docutils literal"><span class="pre">repr1()</span></code></a>. Type-specific methods which need to
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recursively format a value should call <code class="docutils literal"><span class="pre">self.repr1(subobj,</span> <span class="pre">level</span> <span class="pre">-</span> <span class="pre">1)</span></code>.</p>
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<div class="section" id="subclassing-repr-objects">
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<span id="subclassing-reprs"></span><h2>8.19.2. Subclassing Repr Objects<a class="headerlink" href="#subclassing-repr-objects" title="Permalink to this headline">¶</a></h2>
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<p>The use of dynamic dispatching by <a class="reference internal" href="#repr.Repr.repr1" title="repr.Repr.repr1"><code class="xref py py-meth docutils literal"><span class="pre">Repr.repr1()</span></code></a> allows subclasses of
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<a class="reference internal" href="#repr.Repr" title="repr.Repr"><code class="xref py py-class docutils literal"><span class="pre">Repr</span></code></a> to add support for additional built-in object types or to modify
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the handling of types already supported. This example shows how special support
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for file objects could be added:</p>
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<div class="highlight-python"><div class="highlight"><pre><span class="kn">import</span> <span class="nn">repr</span> <span class="kn">as</span> <span class="nn">reprlib</span>
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<span class="kn">import</span> <span class="nn">sys</span>
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<span class="k">class</span> <span class="nc">MyRepr</span><span class="p">(</span><span class="n">reprlib</span><span class="o">.</span><span class="n">Repr</span><span class="p">):</span>
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<span class="k">def</span> <span class="nf">repr_file</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">obj</span><span class="p">,</span> <span class="n">level</span><span class="p">):</span>
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<span class="k">if</span> <span class="n">obj</span><span class="o">.</span><span class="n">name</span> <span class="ow">in</span> <span class="p">[</span><span class="s1">'<stdin>'</span><span class="p">,</span> <span class="s1">'<stdout>'</span><span class="p">,</span> <span class="s1">'<stderr>'</span><span class="p">]:</span>
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<span class="k">return</span> <span class="n">obj</span><span class="o">.</span><span class="n">name</span>
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<span class="k">else</span><span class="p">:</span>
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<span class="k">return</span> <span class="nb">repr</span><span class="p">(</span><span class="n">obj</span><span class="p">)</span>
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<span class="n">aRepr</span> <span class="o">=</span> <span class="n">MyRepr</span><span class="p">()</span>
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<span class="k">print</span> <span class="n">aRepr</span><span class="o">.</span><span class="n">repr</span><span class="p">(</span><span class="n">sys</span><span class="o">.</span><span class="n">stdin</span><span class="p">)</span> <span class="c1"># prints '<stdin>'</span>
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<h3><a href="../contents.html">Table Of Contents</a></h3>
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<li><a class="reference internal" href="#">8.19. <code class="docutils literal"><span class="pre">repr</span></code> — Alternate <code class="docutils literal"><span class="pre">repr()</span></code> implementation</a><ul>
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<li><a class="reference internal" href="#repr-objects">8.19.1. Repr Objects</a></li>
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<li><a class="reference internal" href="#subclassing-repr-objects">8.19.2. Subclassing Repr Objects</a></li>
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