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Commit82ba6ce

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Improve assert_type phrasing (#104081)
I'd like to make the fact that this does nothing at runtimereally obvious, since I suspect this is unintuitive for users who areunfamiliar with static type checking.I thought of this because ofhttps://discuss.python.org/t/add-arg-check-type-to-types/26384wherein I'm skeptical that the user really did want `assert_type`.
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‎Doc/library/typing.rst

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@@ -2484,15 +2484,16 @@ Functions and decorators
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Ask a static type checker to confirm that *val* has an inferred type of *typ*.
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When the type checker encounters a call to ``assert_type()``, it
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At runtime this does nothing: it returns the first argument unchanged with no
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checks or side effects, no matter the actual type of the argument.
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When a static type checker encounters a call to ``assert_type()``, it
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emits an error if the value is not of the specified type::
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def greet(name: str) -> None:
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assert_type(name, str) # OK, inferred type of `name` is `str`
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assert_type(name, int) # type checker error
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At runtime this returns the first argument unchanged with no side effects.
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This function is useful for ensuring the type checker's understanding of a
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script is in line with the developer's intentions::
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‎Lib/typing.py

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@@ -2319,15 +2319,16 @@ def cast(typ, val):
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defassert_type(val,typ,/):
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"""Ask a static type checker to confirm that the value is of the given type.
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When the type checker encounters a call to assert_type(), it
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At runtime this does nothing: it returns the first argument unchanged with no
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checks or side effects, no matter the actual type of the argument.
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When a static type checker encounters a call to assert_type(), it
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emits an error if the value is not of the specified type::
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def greet(name: str) -> None:
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assert_type(name, str) # ok
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assert_type(name, int) # type checker error
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At runtime this returns the first argument unchanged and otherwise
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does nothing.
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"""
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returnval
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