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gh-113255: Clarify docs for typing.reveal_type (#113286)

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Co-authored-by: AlexWaygood <alex.waygood@gmail.com>
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Kir 2023-12-21 02:21:23 +09:00 • committed by GitHub
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2 changed files with 15 additions and 16 deletions
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27
Doc/library/typing.rst
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@ -2604,10 +2604,10 @@ Functions and decorators
.. function:: reveal_type(obj, /) .. function:: reveal_type(obj, /)
Reveal the inferred static type of an expression. Ask a static type checker to reveal the inferred type of an expression.
When a static type checker encounters a call to this function, When a static type checker encounters a call to this function,
it emits a diagnostic with the type of the argument. For example:: it emits a diagnostic with the inferred type of the argument. For example::
x: int = 1 x: int = 1
reveal_type(x) # Revealed type is "builtins.int" reveal_type(x) # Revealed type is "builtins.int"
@ -2615,22 +2615,21 @@ Functions and decorators
This can be useful when you want to debug how your type checker This can be useful when you want to debug how your type checker
handles a particular piece of code. handles a particular piece of code.
The function returns its argument unchanged, which allows using At runtime, this function prints the runtime type of its argument to
it within an expression:: :data:`sys.stderr` and returns the argument unchanged (allowing the call to
be used within an expression)::
x = reveal_type(1) # Revealed type is "builtins.int"
Most type checkers support ``reveal_type()`` anywhere, even if the
name is not imported from ``typing``. Importing the name from
``typing`` allows your code to run without runtime errors and
communicates intent more clearly.
At runtime, this function prints the runtime type of its argument to stderr
and returns it unchanged::
x = reveal_type(1) # prints "Runtime type is int" x = reveal_type(1) # prints "Runtime type is int"
print(x) # prints "1" print(x) # prints "1"
Note that the runtime type may be different from (more or less specific
than) the type statically inferred by a type checker.
Most type checkers support ``reveal_type()`` anywhere, even if the
name is not imported from ``typing``. Importing the name from
``typing``, however, allows your code to run without runtime errors and
communicates intent more clearly.
.. versionadded:: 3.11 .. versionadded:: 3.11
.. decorator:: dataclass_transform(*, eq_default=True, order_default=False, \ .. decorator:: dataclass_transform(*, eq_default=True, order_default=False, \

4
Lib/typing.py
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@ -3301,7 +3301,7 @@ class TextIO(IO[str]):
def reveal_type[T](obj: T, /) -> T: def reveal_type[T](obj: T, /) -> T:
"""Reveal the inferred type of a variable. """Ask a static type checker to reveal the inferred type of an expression.
When a static type checker encounters a call to ``reveal_type()``, When a static type checker encounters a call to ``reveal_type()``,
it will emit the inferred type of the argument:: it will emit the inferred type of the argument::
@ -3313,7 +3313,7 @@ def reveal_type[T](obj: T, /) -> T:
will produce output similar to 'Revealed type is "builtins.int"'. will produce output similar to 'Revealed type is "builtins.int"'.
At runtime, the function prints the runtime type of the At runtime, the function prints the runtime type of the
argument and returns it unchanged. argument and returns the argument unchanged.
""" """
print(f"Runtime type is {type(obj).__name__!r}", file=sys.stderr) print(f"Runtime type is {type(obj).__name__!r}", file=sys.stderr)
return obj return obj