~dkuhlman/python-training-materials/Materials

<h1>26.1. <a class="reference internal" href="#module-typing" title="typing: Support for type hints (see PEP 484)."><code class="xref py py-mod docutils literal">typing</code></a> — Support for type hints<a class="headerlink" href="#module-typing" title="Permalink to this headline">¶</a></h1>

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

This module supports type hints as specified by <a class="pep reference external" href="https://www.python.org/dev/peps/pep-0484">PEP 484</a>. The most

fundamental support consists of the type <a class="reference internal" href="#typing.Any" title="typing.Any"><code class="xref py py-class docutils literal">Any</code></a>, <a class="reference internal" href="#typing.Union" title="typing.Union"><code class="xref py py-class docutils literal">Union</code></a>,

<a class="reference internal" href="#typing.Tuple" title="typing.Tuple"><code class="xref py py-class docutils literal">Tuple</code></a>, <a class="reference internal" href="#typing.Callable" title="typing.Callable"><code class="xref py py-class docutils literal">Callable</code></a>, <a class="reference internal" href="#typing.TypeVar" title="typing.TypeVar"><code class="xref py py-class docutils literal">TypeVar</code></a>, and

<a class="reference internal" href="#typing.Generic" title="typing.Generic"><code class="xref py py-class docutils literal">Generic</code></a>. For full specification please see <a class="pep reference external" href="https://www.python.org/dev/peps/pep-0484">PEP 484</a>. For

a simplified introduction to type hints see <a class="pep reference external" href="https://www.python.org/dev/peps/pep-0483">PEP 483</a>.

The function below takes and returns a string and is annotated as follows:

<div class="highlight-python3"><div class="highlight"><pre>def greeting(name: str) -> str:

return 'Hello ' + name

</pre></div>

</div>

In the function <code class="docutils literal">greeting</code>, the argument <code class="docutils literal">name</code> is expected to be of type

<a class="reference internal" href="stdtypes.html#str" title="str"><code class="xref py py-class docutils literal">str</code></a> and the return type <a class="reference internal" href="stdtypes.html#str" title="str"><code class="xref py py-class docutils literal">str</code></a>. Subtypes are accepted as

arguments.

<h2>26.1.1. Type aliases<a class="headerlink" href="#type-aliases" title="Permalink to this headline">¶</a></h2>

A type alias is defined by assigning the type to the alias:

<div class="highlight-python3"><div class="highlight"><pre>Vector = List[float]

</pre></div>

</div>

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</div>

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<h2>26.1.2. Callable<a class="headerlink" href="#callable" title="Permalink to this headline">¶</a></h2>

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Frameworks expecting callback functions of specific signatures might be

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type hinted using <code class="docutils literal">Callable[[Arg1Type, Arg2Type], ReturnType]</code>.

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For example:

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<div class="highlight-python3"><div class="highlight"><pre>from typing import Callable

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def feeder(get_next_item: Callable[[], str]) -> None:

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# Body

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def async_query(on_success: Callable[[int], None],

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on_error: Callable[[int, Exception], None]) -> None:

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# Body

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</pre></div>

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</div>

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It is possible to declare the return type of a callable without specifying

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the call signature by substituting a literal ellipsis

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for the list of arguments in the type hint: <code class="docutils literal">Callable[..., ReturnType]</code>.

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<code class="docutils literal">None</code> as a type hint is a special case and is replaced by <code class="docutils literal">type(None)</code>.

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</div>

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<h2>26.1.3. Generics<a class="headerlink" href="#generics" title="Permalink to this headline">¶</a></h2>

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Since type information about objects kept in containers cannot be statically

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inferred in a generic way, abstract base classes have been extended to support

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subscription to denote expected types for container elements.

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<div class="highlight-python3"><div class="highlight"><pre>from typing import Mapping, Sequence

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def notify_by_email(employees: Sequence[Employee],

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overrides: Mapping[str, str]) -> None: ...

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</pre></div>

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</div>

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Generics can be parametrized by using a new factory available in typing

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called <a class="reference internal" href="#typing.TypeVar" title="typing.TypeVar"><code class="xref py py-class docutils literal">TypeVar</code></a>.

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<div class="highlight-python3"><div class="highlight"><pre>from typing import Sequence, TypeVar

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T = TypeVar('T') # Declare type variable

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def first(l: Sequence[T]) -> T: # Generic function

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return l[0]

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</pre></div>

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</div>

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</div>

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<h2>26.1.4. User-defined generic types<a class="headerlink" href="#user-defined-generic-types" title="Permalink to this headline">¶</a></h2>

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A user-defined class can be defined as a generic class.

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<div class="highlight-python3"><div class="highlight"><pre>from typing import TypeVar, Generic

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from logging import Logger

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T = TypeVar('T')

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class LoggedVar(Generic[T]):

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def __init__(self, value: T, name: str, logger: Logger) -> None:

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self.name = name

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self.logger = logger

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self.value = value

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def set(self, new: T) -> None:

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self.log('Set ' + repr(self.value))

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self.value = new

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def get(self) -> T:

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self.log('Get ' + repr(self.value))

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return self.value

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def log(self, message: str) -> None:

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self.logger.info('{}: {}'.format(self.name, message))

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</pre></div>

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</div>

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<code class="docutils literal">Generic[T]</code> as a base class defines that the class <code class="docutils literal">LoggedVar</code> takes a

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single type parameter <code class="docutils literal">T</code> . This also makes <code class="docutils literal">T</code> valid as a type within the

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class body.

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The <a class="reference internal" href="#typing.Generic" title="typing.Generic"><code class="xref py py-class docutils literal">Generic</code></a> base class uses a metaclass that defines

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<a class="reference internal" href="../reference/datamodel.html#object.__getitem__" title="object.__getitem__"><code class="xref py py-meth docutils literal">__getitem__()</code></a> so that <code class="docutils literal">LoggedVar[t]</code> is valid as a type:

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<div class="highlight-python3"><div class="highlight"><pre>from typing import Iterable

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def zero_all_vars(vars: Iterable[LoggedVar[int]]) -> None:

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for var in vars:

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var.set(0)

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</pre></div>

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</div>

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A generic type can have any number of type variables, and type variables may

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be constrained:

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<div class="highlight-python3"><div class="highlight"><pre>from typing import TypeVar, Generic

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...

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T = TypeVar('T')

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S = TypeVar('S', int, str)

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class StrangePair(Generic[T, S]):

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...

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</pre></div>

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</div>

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Each type variable argument to <a class="reference internal" href="#typing.Generic" title="typing.Generic"><code class="xref py py-class docutils literal">Generic</code></a> must be distinct.

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This is thus invalid:

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<div class="highlight-python3"><div class="highlight"><pre>from typing import TypeVar, Generic

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...

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T = TypeVar('T')

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class Pair(Generic[T, T]): # INVALID

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...

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</pre></div>

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</div>

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You can use multiple inheritance with <a class="reference internal" href="#typing.Generic" title="typing.Generic"><code class="xref py py-class docutils literal">Generic</code></a>:

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<div class="highlight-python3"><div class="highlight"><pre>from typing import TypeVar, Generic, Sized

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T = TypeVar('T')

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class LinkedList(Sized, Generic[T]):

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...

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</pre></div>

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</div>

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When inheriting from generic classes, some type variables could fixed:

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<div class="highlight-python3"><div class="highlight"><pre>from typing import TypeVar, Mapping

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T = TypeVar('T')

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class MyDict(Mapping[str, T]):

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...

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</pre></div>

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</div>

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In this case <code class="docutils literal">MyDict</code> has a single parameter, <code class="docutils literal">T</code>.

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Subclassing a generic class without specifying type parameters assumes

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<a class="reference internal" href="#typing.Any" title="typing.Any"><code class="xref py py-class docutils literal">Any</code></a> for each position. In the following example, <code class="docutils literal">MyIterable</code> is

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not generic but implicitly inherits from <code class="docutils literal">Iterable[Any]</code>:

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<div class="highlight-python3"><div class="highlight"><pre>from typing import Iterable

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class MyIterable(Iterable): # Same as Iterable[Any]

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</pre></div>

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</div>

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The metaclass used by <a class="reference internal" href="#typing.Generic" title="typing.Generic"><code class="xref py py-class docutils literal">Generic</code></a> is a subclass of <a class="reference internal" href="abc.html#abc.ABCMeta" title="abc.ABCMeta"><code class="xref py py-class docutils literal">abc.ABCMeta</code></a>.

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A generic class can be an ABC by including abstract methods or properties,

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and generic classes can also have ABCs as base classes without a metaclass

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conflict. Generic metaclasses are not supported.

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</div>

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A special kind of type is <a class="reference internal" href="#typing.Any" title="typing.Any"><code class="xref py py-class docutils literal">Any</code></a>. Every type is a subtype of

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<a class="reference internal" href="#typing.Any" title="typing.Any"><code class="xref py py-class docutils literal">Any</code></a>. This is also true for the builtin type object. However, to the

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static type checker these are completely different.

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When the type of a value is <a class="reference internal" href="functions.html#object" title="object"><code class="xref py py-class docutils literal">object</code></a>, the type checker will reject

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almost all operations on it, and assigning it to a variable (or using it as a

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return value) of a more specialized type is a type error. On the other hand,

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when a value has type <a class="reference internal" href="#typing.Any" title="typing.Any"><code class="xref py py-class docutils literal">Any</code></a>, the type checker will allow all operations

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on it, and a value of type <a class="reference internal" href="#typing.Any" title="typing.Any"><code class="xref py py-class docutils literal">Any</code></a> can be assigned to a variable (or used

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as a return value) of a more constrained type.

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</div>

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<h2>26.1.6. Classes, functions, and decorators<a class="headerlink" href="#classes-functions-and-decorators" title="Permalink to this headline">¶</a></h2>

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The module defines the following classes, functions and decorators:

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

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<dd>Special type indicating an unconstrained type.

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<li>Any object is an instance of <a class="reference internal" href="#typing.Any" title="typing.Any"><code class="xref py py-class docutils literal">Any</code></a>.</li>

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<li>Any class is a subclass of <a class="reference internal" href="#typing.Any" title="typing.Any"><code class="xref py py-class docutils literal">Any</code></a>.</li>

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<li>As a special case, <a class="reference internal" href="#typing.Any" title="typing.Any"><code class="xref py py-class docutils literal">Any</code></a> and <a class="reference internal" href="functions.html#object" title="object"><code class="xref py py-class docutils literal">object</code></a> are subclasses of

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each other.</li>

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</ul>

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</dd></dl>

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

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<dd>Type variable.

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Usage:

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<div class="highlight-python3"><div class="highlight"><pre>T = TypeVar('T') # Can be anything

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A = TypeVar('A', str, bytes) # Must be str or bytes

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</pre></div>

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</div>

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Type variables exist primarily for the benefit of static type

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checkers. They serve as the parameters for generic types as well

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as for generic function definitions. See class Generic for more

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information on generic types. Generic functions work as follows:

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<div class="highlight-python3"><div class="highlight"><pre>def repeat(x: T, n: int) -> Sequence[T]:

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"""Return a list containing n references to x."""

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return [x]*n

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def longest(x: A, y: A) -> A:

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"""Return the longest of two strings."""

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return x if len(x) >= len(y) else y

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</pre></div>

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</div>

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The latter example’s signature is essentially the overloading

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of <code class="docutils literal">(str, str) -> str</code> and <code class="docutils literal">(bytes, bytes) -> bytes</code>. Also note

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that if the arguments are instances of some subclass of <a class="reference internal" href="stdtypes.html#str" title="str"><code class="xref py py-class docutils literal">str</code></a>,

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the return type is still plain <a class="reference internal" href="stdtypes.html#str" title="str"><code class="xref py py-class docutils literal">str</code></a>.

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At runtime, <code class="docutils literal">isinstance(x, T)</code> will raise <a class="reference internal" href="exceptions.html#TypeError" title="TypeError"><code class="xref py py-exc docutils literal">TypeError</code></a>. In general,

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<a class="reference internal" href="functions.html#isinstance" title="isinstance"><code class="xref py py-func docutils literal">isinstance()</code></a> and <a class="reference internal" href="functions.html#issubclass" title="issubclass"><code class="xref py py-func docutils literal">issubclass()</code></a> should not be used with types.

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Type variables may be marked covariant or contravariant by passing

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<code class="docutils literal">covariant=True</code> or <code class="docutils literal">contravariant=True</code>. See <a class="pep reference external" href="https://www.python.org/dev/peps/pep-0484">PEP 484</a> for more

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details. By default type variables are invariant. Alternatively,

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a type variable may specify an upper bound using <code class="docutils literal">bound=<type></code>.

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This means that an actual type substituted (explicitly or implicitly)

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for the type variable must be a subclass of the boundary type,

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see <a class="pep reference external" href="https://www.python.org/dev/peps/pep-0484">PEP 484</a>.

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</dd></dl>

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

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<dd>Union type; <code class="docutils literal">Union[X, Y]</code> means either X or Y.

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To define a union, use e.g. <code class="docutils literal">Union[int, str]</code>. Details:

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<ul>

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<li>The arguments must be types and there must be at least one.

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</li>

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<li>Unions of unions are flattened, e.g.:

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<div class="highlight-python3"><div class="highlight"><pre>Union[Union[int, str], float] == Union[int, str, float]

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</pre></div>

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</div>

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</li>

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<li>Unions of a single argument vanish, e.g.:

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<div class="highlight-python3"><div class="highlight"><pre>Union[int] == int # The constructor actually returns int

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</pre></div>

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</div>

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</li>

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<li>Redundant arguments are skipped, e.g.:

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<div class="highlight-python3"><div class="highlight"><pre>Union[int, str, int] == Union[int, str]

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</pre></div>

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</div>

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</li>

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<li>When comparing unions, the argument order is ignored, e.g.:

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<div class="highlight-python3"><div class="highlight"><pre>Union[int, str] == Union[str, int]

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</pre></div>

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</div>

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</li>

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<li>If <a class="reference internal" href="#typing.Any" title="typing.Any"><code class="xref py py-class docutils literal">Any</code></a> is present it is the sole survivor, e.g.:

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</pre></div>

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</div>

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</li>

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<li>You cannot subclass or instantiate a union.

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</li>

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<li>You cannot write <code class="docutils literal">Union[X][Y]</code>.

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</li>

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<li>You can use <code class="docutils literal">Optional[X]</code> as a shorthand for <code class="docutils literal">Union[X, None]</code>.

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</li>

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</ul>

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</dd></dl>

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

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<dd>Optional type.

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<code class="docutils literal">Optional[X]</code> is equivalent to <code class="docutils literal">Union[X, type(None)]</code>.

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Note that this is not the same concept as an optional argument,

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which is one that has a default. An optional argument with a

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default needn’t use the <code class="docutils literal">Optional</code> qualifier on its type

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annotation (although it is inferred if the default is <code class="docutils literal">None</code>).

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A mandatory argument may still have an <code class="docutils literal">Optional</code> type if an

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explicit value of <code class="docutils literal">None</code> is allowed.

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</dd></dl>

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

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<dd>Tuple type; <code class="docutils literal">Tuple[X, Y]</code> is the is the type of a tuple of two items

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with the first item of type X and the second of type Y.

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Example: <code class="docutils literal">Tuple[T1, T2]</code> is a tuple of two elements corresponding

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to type variables T1 and T2. <code class="docutils literal">Tuple[int, float, str]</code> is a tuple

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of an int, a float and a string.

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To specify a variable-length tuple of homogeneous type,

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use literal ellipsis, e.g. <code class="docutils literal">Tuple[int, ...]</code>.

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</dd></dl>

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

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<dd>Callable type; <code class="docutils literal">Callable[[int], str]</code> is a function of (int) -> str.

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The subscription syntax must always be used with exactly two

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values: the argument list and the return type. The argument list

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must be a list of types; the return type must be a single type.

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There is no syntax to indicate optional or keyword arguments,

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such function types are rarely used as callback types.

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<code class="docutils literal">Callable[..., ReturnType]</code> could be used to type hint a callable

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taking any number of arguments and returning <code class="docutils literal">ReturnType</code>.

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A plain <a class="reference internal" href="#typing.Callable" title="typing.Callable"><code class="xref py py-class docutils literal">Callable</code></a> is equivalent to <code class="docutils literal">Callable[..., Any]</code>.

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</dd></dl>

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

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<dd>Abstract base class for generic types.

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A generic type is typically declared by inheriting from an

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instantiation of this class with one or more type variables.

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For example, a generic mapping type might be defined as:

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<div class="highlight-python3"><div class="highlight"><pre>class Mapping(Generic[KT, VT]):

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def __getitem__(self, key: KT) -> VT:

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...

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# Etc.

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</pre></div>

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</div>

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This class can then be used as follows:

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<div class="highlight-python3"><div class="highlight"><pre>X = TypeVar('X')

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Y = TypeVar('Y')

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def lookup_name(mapping: Mapping[X, Y], key: X, default: Y) -> Y:

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try:

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return mapping[key]

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except KeyError:

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return default

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</pre></div>

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</div>

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</dd></dl>

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class <code class="descclassname">typing.</code><code class="descname">Iterable</code>(Generic[T_co])<a class="headerlink" href="#typing.Iterable" title="Permalink to this definition">¶</a></dt>

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<dd>A generic version of the <a class="reference internal" href="collections.abc.html#collections.abc.Iterable" title="collections.abc.Iterable"><code class="xref py py-class docutils literal">collections.abc.Iterable</code></a>.

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</dd></dl>

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class <code class="descclassname">typing.</code><code class="descname">Iterator</code>(Iterable[T_co])<a class="headerlink" href="#typing.Iterator" title="Permalink to this definition">¶</a></dt>

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<dd>A generic version of the <a class="reference internal" href="collections.abc.html#collections.abc.Iterator" title="collections.abc.Iterator"><code class="xref py py-class docutils literal">collections.abc.Iterator</code></a>.

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</dd></dl>

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

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<dd>An ABC with one abstract method <code class="docutils literal">__int__</code>.

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</dd></dl>

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

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<dd>An ABC with one abstract method <code class="docutils literal">__float__</code>.

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</dd></dl>

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

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<dd>An ABC with one abstract method <code class="docutils literal">__abs__</code> that is covariant

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in its return type.

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</dd></dl>

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

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<dd>An ABC with one abstract method <code class="docutils literal">__round__</code>

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that is covariant in its return type.

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</dd></dl>

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

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<dd>An ABC with one abstract method <code class="docutils literal">__reversed__</code> returning

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an <code class="docutils literal">Iterator[T_co]</code>.

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</dd></dl>

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class <code class="descclassname">typing.</code><code class="descname">Container</code>(Generic[T_co])<a class="headerlink" href="#typing.Container" title="Permalink to this definition">¶</a></dt>

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<dd>A generic version of <a class="reference internal" href="collections.abc.html#collections.abc.Container" title="collections.abc.Container"><code class="xref py py-class docutils literal">collections.abc.Container</code></a>.

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</dd></dl>

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class <code class="descclassname">typing.</code><code class="descname">AbstractSet</code>(Sized, Iterable[T_co], Container[T_co])<a class="headerlink" href="#typing.AbstractSet" title="Permalink to this definition">¶</a></dt>

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<dd>A generic version of <a class="reference internal" href="collections.abc.html#collections.abc.Set" title="collections.abc.Set"><code class="xref py py-class docutils literal">collections.abc.Set</code></a>.

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</dd></dl>

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class <code class="descclassname">typing.</code><code class="descname">MutableSet</code>(AbstractSet[T])<a class="headerlink" href="#typing.MutableSet" title="Permalink to this definition">¶</a></dt>

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<dd>A generic version of <a class="reference internal" href="collections.abc.html#collections.abc.MutableSet" title="collections.abc.MutableSet"><code class="xref py py-class docutils literal">collections.abc.MutableSet</code></a>.

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</dd></dl>

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class <code class="descclassname">typing.</code><code class="descname">Mapping</code>(Sized, Iterable[KT], Container[KT], Generic[VT_co])<a class="headerlink" href="#typing.Mapping" title="Permalink to this definition">¶</a></dt>

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<dd>A generic version of <a class="reference internal" href="collections.abc.html#collections.abc.Mapping" title="collections.abc.Mapping"><code class="xref py py-class docutils literal">collections.abc.Mapping</code></a>.

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</dd></dl>

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class <code class="descclassname">typing.</code><code class="descname">MutableMapping</code>(Mapping[KT, VT])<a class="headerlink" href="#typing.MutableMapping" title="Permalink to this definition">¶</a></dt>

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<dd>A generic version of <a class="reference internal" href="collections.abc.html#collections.abc.MutableMapping" title="collections.abc.MutableMapping"><code class="xref py py-class docutils literal">collections.abc.MutableMapping</code></a>.

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</dd></dl>

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class <code class="descclassname">typing.</code><code class="descname">Sequence</code>(Sized, Iterable[T_co], Container[T_co])<a class="headerlink" href="#typing.Sequence" title="Permalink to this definition">¶</a></dt>

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<dd>A generic version of <a class="reference internal" href="collections.abc.html#collections.abc.Sequence" title="collections.abc.Sequence"><code class="xref py py-class docutils literal">collections.abc.Sequence</code></a>.

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</dd></dl>

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class <code class="descclassname">typing.</code><code class="descname">MutableSequence</code>(Sequence[T])<a class="headerlink" href="#typing.MutableSequence" title="Permalink to this definition">¶</a></dt>

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<dd>A generic version of <a class="reference internal" href="collections.abc.html#collections.abc.MutableSequence" title="collections.abc.MutableSequence"><code class="xref py py-class docutils literal">collections.abc.MutableSequence</code></a>.

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</dd></dl>

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class <code class="descclassname">typing.</code><code class="descname">ByteString</code>(Sequence[int])<a class="headerlink" href="#typing.ByteString" title="Permalink to this definition">¶</a></dt>

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<dd>A generic version of <code class="xref py py-class docutils literal">collections.abc.ByteString</code>.

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This type represents the types <a class="reference internal" href="functions.html#bytes" title="bytes"><code class="xref py py-class docutils literal">bytes</code></a>, <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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and <a class="reference internal" href="stdtypes.html#memoryview" title="memoryview"><code class="xref py py-class docutils literal">memoryview</code></a>.

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As a shorthand for this type, <a class="reference internal" href="functions.html#bytes" title="bytes"><code class="xref py py-class docutils literal">bytes</code></a> can be used to

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annotate arguments of any of the types mentioned above.

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</dd></dl>

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class <code class="descclassname">typing.</code><code class="descname">List</code>(list, MutableSequence[T])<a class="headerlink" href="#typing.List" title="Permalink to this definition">¶</a></dt>

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<dd>Generic version of <a class="reference internal" href="stdtypes.html#list" title="list"><code class="xref py py-class docutils literal">list</code></a>.

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Useful for annotating return types. To annotate arguments it is preferred

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to use abstract collection types such as <a class="reference internal" href="#typing.Mapping" title="typing.Mapping"><code class="xref py py-class docutils literal">Mapping</code></a>, <a class="reference internal" href="#typing.Sequence" title="typing.Sequence"><code class="xref py py-class docutils literal">Sequence</code></a>,

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or <a class="reference internal" href="#typing.AbstractSet" title="typing.AbstractSet"><code class="xref py py-class docutils literal">AbstractSet</code></a>.

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This type may be used as follows:

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def vec2(x: T, y: T) -> List[T]:

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return [x, y]

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def slice__to_4(vector: Sequence[T]) -> List[T]:

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return vector[0:4]

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</pre></div>

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</div>

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</dd></dl>

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<dt>

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class <code class="descclassname">typing.</code><code class="descname">AbstractSet</code>(set, MutableSet[T])</dt>

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</dd></dl>

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class <code class="descclassname">typing.</code><code class="descname">MappingView</code>(Sized, Iterable[T_co])<a class="headerlink" href="#typing.MappingView" title="Permalink to this definition">¶</a></dt>

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<dd>A generic version of <a class="reference internal" href="collections.abc.html#collections.abc.MappingView" title="collections.abc.MappingView"><code class="xref py py-class docutils literal">collections.abc.MappingView</code></a>.

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</dd></dl>

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class <code class="descclassname">typing.</code><code class="descname">KeysView</code>(MappingView[KT_co], AbstractSet[KT_co])<a class="headerlink" href="#typing.KeysView" title="Permalink to this definition">¶</a></dt>

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<dd>A generic version of <a class="reference internal" href="collections.abc.html#collections.abc.KeysView" title="collections.abc.KeysView"><code class="xref py py-class docutils literal">collections.abc.KeysView</code></a>.

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</dd></dl>

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class <code class="descclassname">typing.</code><code class="descname">ItemsView</code>(MappingView, Generic[KT_co, VT_co])<a class="headerlink" href="#typing.ItemsView" title="Permalink to this definition">¶</a></dt>

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<dd>A generic version of <a class="reference internal" href="collections.abc.html#collections.abc.ItemsView" title="collections.abc.ItemsView"><code class="xref py py-class docutils literal">collections.abc.ItemsView</code></a>.

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</dd></dl>

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class <code class="descclassname">typing.</code><code class="descname">ValuesView</code>(MappingView[VT_co])<a class="headerlink" href="#typing.ValuesView" title="Permalink to this definition">¶</a></dt>

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<dd>A generic version of <a class="reference internal" href="collections.abc.html#collections.abc.ValuesView" title="collections.abc.ValuesView"><code class="xref py py-class docutils literal">collections.abc.ValuesView</code></a>.

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</dd></dl>

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class <code class="descclassname">typing.</code><code class="descname">Dict</code>(dict, MutableMapping[KT, VT])<a class="headerlink" href="#typing.Dict" title="Permalink to this definition">¶</a></dt>

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<dd>A generic version of <a class="reference internal" href="stdtypes.html#dict" title="dict"><code class="xref py py-class docutils literal">dict</code></a>.

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The usage of this type is as follows:

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<div class="highlight-python3"><div class="highlight"><pre>def get_position_in_index(word_list: Dict[str, int], word: str) -> int:

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return word_list[word]

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</pre></div>

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</div>

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</dd></dl>

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class <code class="descclassname">typing.</code><code class="descname">Generator</code>(Iterator[T_co], Generic[T_co, T_contra, V_co])<a class="headerlink" href="#typing.Generator" title="Permalink to this definition">¶</a></dt>

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

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<dd>Wrapper namespace for I/O stream types.

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This defines the generic type <code class="docutils literal">IO[AnyStr]</code> and aliases <code class="docutils literal">TextIO</code>

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and <code class="docutils literal">BinaryIO</code> for respectively <code class="docutils literal">IO[str]</code> and <code class="docutils literal">IO[bytes]</code>.

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These representing the types of I/O streams such as returned by

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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>.

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</dd></dl>

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

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<dd>Wrapper namespace for regular expression matching types.

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This defines the type aliases <code class="docutils literal">Pattern</code> and <code class="docutils literal">Match</code> which

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correspond to the return types from <a class="reference internal" href="re.html#re.compile" title="re.compile"><code class="xref py py-func docutils literal">re.compile()</code></a> and

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<a class="reference internal" href="re.html#re.match" title="re.match"><code class="xref py py-func docutils literal">re.match()</code></a>. These types (and the corresponding functions)

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are generic in <code class="docutils literal">AnyStr</code> and can be made specific by writing

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<code class="docutils literal">Pattern[str]</code>, <code class="docutils literal">Pattern[bytes]</code>, <code class="docutils literal">Match[str]</code>, or

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<code class="docutils literal">Match[bytes]</code>.

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</dd></dl>

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<code class="descclassname">typing.</code><code class="descname">NamedTuple</code>(typename, fields)<a class="headerlink" href="#typing.NamedTuple" title="Permalink to this definition">¶</a></dt>

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<dd>Typed version of namedtuple.

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Usage:

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<div class="highlight-python3"><div class="highlight"><pre>Employee = typing.NamedTuple('Employee', [('name', str), ('id', int)])

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</pre></div>

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</div>

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This is equivalent to:

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<div class="highlight-python3"><div class="highlight"><pre>Employee = collections.namedtuple('Employee', ['name', 'id'])

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</pre></div>

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</div>

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The resulting class has one extra attribute: _field_types,

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giving a dict mapping field names to types. (The field names

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are in the _fields attribute, which is part of the namedtuple

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API.)

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</dd></dl>

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<code class="descclassname">typing.</code><code class="descname">cast</code>(typ, val)<a class="headerlink" href="#typing.cast" title="Permalink to this definition">¶</a></dt>

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<dd>Cast a value to a type.

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This returns the value unchanged. To the type checker this

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signals that the return value has the designated type, but at

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runtime we intentionally don’t check anything (we want this

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to be as fast as possible).

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</dd></dl>

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<code class="descclassname">typing.</code><code class="descname">get_type_hints</code>(obj)<a class="headerlink" href="#typing.get_type_hints" title="Permalink to this definition">¶</a></dt>

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<dd>Return type hints for a function or method object.

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This is often the same as <code class="docutils literal">obj.__annotations__</code>, but it handles

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forward references encoded as string literals, and if necessary

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adds <code class="docutils literal">Optional[t]</code> if a default value equal to None is set.

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</dd></dl>

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<code class="descclassname">@</code><code class="descclassname">typing.</code><code class="descname">no_type_check</code>(arg)<a class="headerlink" href="#typing.no_type_check" title="Permalink to this definition">¶</a></dt>

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<dd>Decorator to indicate that annotations are not type hints.

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The argument must be a class or function; if it is a class, it

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applies recursively to all methods defined in that class (but not

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to methods defined in its superclasses or subclasses).

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This mutates the function(s) in place.

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</dd></dl>

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<code class="descclassname">@</code><code class="descclassname">typing.</code><code class="descname">no_type_check_decorator</code>(decorator)<a class="headerlink" href="#typing.no_type_check_decorator" title="Permalink to this definition">¶</a></dt>

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<dd>Decorator to give another decorator the <a class="reference internal" href="#typing.no_type_check" title="typing.no_type_check"><code class="xref py py-func docutils literal">no_type_check()</code></a> effect.

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This wraps the decorator with something that wraps the decorated

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function in <a class="reference internal" href="#typing.no_type_check" title="typing.no_type_check"><code class="xref py py-func docutils literal">no_type_check()</code></a>.

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</dd></dl>

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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="#">26.1. <code class="docutils literal">typing</code> — Support for type hints</a><ul>

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<li><a class="reference internal" href="#type-aliases">26.1.1. Type aliases</a></li>

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<li><a class="reference internal" href="#callable">26.1.2. Callable</a></li>

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<li><a class="reference internal" href="#generics">26.1.3. Generics</a></li>

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<li><a class="reference internal" href="#user-defined-generic-types">26.1.4. User-defined generic types</a></li>

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<li><a class="reference internal" href="#classes-functions-and-decorators">26.1.6. Classes, functions, and decorators</a></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="development.html"

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title="previous chapter">26. Development Tools</a>

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<h4>Next topic</h4>

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<a href="pydoc.html"

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title="next chapter">26.2. <code class="docutils literal">pydoc</code> — Documentation generator and online help system</a>

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

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

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

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</ul>

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<h3>Quick search</h3>

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</form>

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Enter search terms or a module, class or function name.

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</div>

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</div>

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<h3>Navigation</h3>

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<ul>

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<a href="../genindex.html" title="General Index"

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>index</a></li>

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<a href="../py-modindex.html" title="Python Module Index"

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>modules</a> |</li>

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<a href="pydoc.html" title="26.2. pydoc — Documentation generator and online help system"

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<li class="nav-item nav-item-1"><a href="index.html" >The Python Standard Library</a> »</li>

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<li class="nav-item nav-item-2"><a href="development.html" >26. Development Tools</a> »</li>

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The Python Software Foundation is a non-profit corporation.

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<a href="../bugs.html">Found a bug</a>?

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