1 from typing import Any, Callable, Text, TypeVar
    2 from decorator import decorate, decorator
    3
    4
    5 MYPY = False
    6
    7 F = TypeVar('F', bound=Callable[..., Any])
    8
    9 @decorator
   10 def print_foo_before(func, *args, **kwargs):
   11     # type: (F, *Any, **Any) -> None
   12     print('foo')
   13     func(*args, **kwargs)
   14
   15 @print_foo_before
   16 def greet(message):
   17     # type: (Text) -> Text
   18     print(message)
   19     return message
   20
   21 greet('bar')
   22 greet(1)
   23
   24 def _memoize(func, *args, **kw):
   25     # type: (F, *Any, **Any) -> F
   26     return func(*args, **kw)
   27
   28 def memoize(f):
   29     # type: (F) -> F
   30     """
   31     A simple memoize implementation. It works by adding a .cache dictionary
   32     to the decorated function. The cache will grow indefinitely, so it is
   33     your responsibility to clear it, if needed.
   34     """
   35     f.cache = {}  # type: ignore
   36     decorated = decorate(f, _memoize)
   37     if MYPY:
   38         reveal_type(decorated)
   39     return decorated
   40
   41 if MYPY:
   42     reveal_type(greet)
   43     reveal_type(memoize(greet))
   44
   45 from decorator import getfullargspec
   46 if MYPY:
   47     reveal_type(getfullargspec)

$ python test.py
foo
bar
foo
1

$ mypy test.py --custom-typeshed-dir=/Users/rafblecher/typeshed-dev --disallow-untyped-decorators
test.py:22: error: Argument 1 to "greet" has incompatible type "int"; expected "str"
test.py:38: error: Revealed type is 'F`-1'
test.py:42: error: Revealed type is 'def (message: builtins.str) -> builtins.str'
test.py:43: error: Revealed type is 'def (message: builtins.str) -> builtins.str'
test.py:47: error: Revealed type is 'def (builtins.object) -> Tuple[builtins.list[builtins.str], Union[builtins.str, None], Union[builtins.str, None], builtins.tuple[Any], builtins.list[builtins.str], builtins.dict[builtins.str, Any], builtins.dict[builtins.str, Any], fallback=decorator.FullArgSpec]'