diff options
Diffstat (limited to 'Doc')
| -rw-r--r-- | Doc/library/typing.rst | 25 |
1 files changed, 25 insertions, 0 deletions
diff --git a/Doc/library/typing.rst b/Doc/library/typing.rst index c7c2cd6..57979cb 100644 --- a/Doc/library/typing.rst +++ b/Doc/library/typing.rst @@ -2148,6 +2148,31 @@ Functions and decorators runtime we intentionally don't check anything (we want this to be as fast as possible). +.. function:: assert_type(val, typ, /) + + Assert (to the type checker) that *val* has an inferred type of *typ*. + + 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, 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:: + + def complex_function(arg: object): + # Do some complex type-narrowing logic, + # after which we hope the inferred type will be `int` + ... + # Test whether the type checker correctly understands our function + assert_type(arg, int) + + .. versionadded:: 3.11 + .. function:: assert_never(arg, /) Assert to the type checker that a line of code is unreachable. |