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JelleZijlstra merged 9 commits into from
Mar 17, 2022
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bpo-46480: add typing.assert_type #30843

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bpo-46480: add typing.assert_type
JelleZijlstra Jan 24, 2022
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Merge branch 'main' into asserttype
JelleZijlstra Feb 2, 2022
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feedback from David Foster
JelleZijlstra Feb 2, 2022
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Merge branch 'main' into asserttype
JelleZijlstra Mar 10, 2022
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Merge remote-tracking branch 'upstream/main' into asserttype
JelleZijlstra Mar 12, 2022
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JelleZijlstra Mar 12, 2022
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JelleZijlstra Mar 12, 2022
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Update Lib/typing.py
JelleZijlstra Mar 12, 2022
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Update Doc/library/typing.rst
JelleZijlstra Mar 12, 2022
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Co-authored-by: Alex Waygood <Alex.Waygood@Gmail.com>
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@JelleZijlstra @AlexWaygood
JelleZijlstra and AlexWaygood authored Mar 12, 2022
commit 49765d3e478886dc687af3abb025150f9f39e254
7 changes: 3 additions & 4 deletions Doc/library/typing.rst
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Expand Up @@ -2116,17 +2116,16 @@ Functions and decorators

.. function:: assert_type(val, typ, /)

Assert (to the type checker) that the value is of the given type.
Assert (to the type checker) that *value* has an inferred type of *type*.

When the type checker encounters a call to ``assert_type()``, it
emits an error if the value is not of the specified type::

def greet(name: str) -> None:
assert_type(name, str) # ok
assert_type(name, str) # OK, inferred type of `name` is `str`
assert_type(name, int) # type checker error

At runtime this returns the first argument unchanged and otherwise
does nothing.
At runtime this returns the first argument unchanged with no side effects.

This function is useful for ensuring the type checker's understanding of a
script is in line with the developer's intentions::
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