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[3.11] Improve assert_type phrasing (GH-104081) (#104084)

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Improve assert_type phrasing (GH-104081)

I'd like to make the fact that this does nothing at runtime
really obvious, since I suspect this is unintuitive for users who are
unfamiliar with static type checking.

I thought of this because of
https://discuss.python.org/t/add-arg-check-type-to-types/26384
wherein I'm skeptical that the user really did want `assert_type`.
(cherry picked from commit 82ba6ce303)

Co-authored-by: Shantanu <12621235+hauntsaninja@users.noreply.github.com>
This commit is contained in:
Miss Islington (bot) 2023-05-02 00:44:16 -07:00 • committed by GitHub
parent 0d40264325
commit 3e7e50e656
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2 changed files with 8 additions and 6 deletions
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7
Lib/typing.py
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@ -2250,15 +2250,16 @@ def cast(typ, val):
def assert_type(val, typ, /):
"""Ask a static type checker to confirm that the value is of the given type.
When the type checker encounters a call to assert_type(), it
At runtime this does nothing: it returns the first argument unchanged with no
checks or side effects, no matter the actual type of the argument.
When a static 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, int) # type checker error
At runtime this returns the first argument unchanged and otherwise
does nothing.
"""
return val