2006-3107-Function-Annotations

This PEP introduces a syntax for adding arbitrary metadata annotations to Python functions

Parameters

def foo(a: expression, b: expression = 5):
    ...

All annotation expressions are evaluated when the function definition is executed, just like default values

def foo(*args: expression, **kwargs: expression):
    ...

Return Values

def sum() -> expression:
    ...

Accessing Function Annotations

Once compiled, a function’s annotations are available via the function’s __annotations__ attribute. This attribute is a mutable dictionary, mapping parameter names to an object representing the evaluated annotation expression