diff options
| -rw-r--r-- | Doc/library/typing.rst | 7 | ||||
| -rw-r--r-- | Lib/typing.py | 7 |
2 files changed, 8 insertions, 6 deletions
diff --git a/Doc/library/typing.rst b/Doc/library/typing.rst index 409a95d528..c22fc0b28a 100644 --- a/Doc/library/typing.rst +++ b/Doc/library/typing.rst @@ -2484,15 +2484,16 @@ Functions and decorators Ask a static type checker to confirm that *val* has an inferred type of *typ*. - 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, inferred type of `name` is `str` assert_type(name, int) # type checker error - 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:: diff --git a/Lib/typing.py b/Lib/typing.py index 1a1c989dba..0dacdd9031 100644 --- a/Lib/typing.py +++ b/Lib/typing.py @@ -2319,15 +2319,16 @@ 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 |