Coverage for /pythoncovmergedfiles/medio/medio/usr/local/lib/python3.8/site-packages/pkg_resources/_vendor/packaging/_typing.py: 0%

1"""For neatly implementing static typing in packaging. 

2 

3`mypy` - the static type analysis tool we use - uses the `typing` module, which 

4provides core functionality fundamental to mypy's functioning. 

5 

6Generally, `typing` would be imported at runtime and used in that fashion - 

7it acts as a no-op at runtime and does not have any run-time overhead by 

8design. 

9 

10As it turns out, `typing` is not vendorable - it uses separate sources for 

11Python 2/Python 3. Thus, this codebase can not expect it to be present. 

12To work around this, mypy allows the typing import to be behind a False-y 

13optional to prevent it from running at runtime and type-comments can be used 

14to remove the need for the types to be accessible directly during runtime. 

15 

16This module provides the False-y guard in a nicely named fashion so that a 

17curious maintainer can reach here to read this. 

18 

19In packaging, all static-typing related imports should be guarded as follows: 

20 

21 from packaging._typing import TYPE_CHECKING 

22 

23 if TYPE_CHECKING: 

24 from typing import ... 

25 

26Ref: https://github.com/python/mypy/issues/3216 

27""" 

28 

29__all__ = ["TYPE_CHECKING", "cast"] 

30 

31# The TYPE_CHECKING constant defined by the typing module is False at runtime 

32# but True while type checking. 

33if False: # pragma: no cover 

34 from typing import TYPE_CHECKING 

35else: 

36 TYPE_CHECKING = False 

37 

38# typing's cast syntax requires calling typing.cast at runtime, but we don't 

39# want to import typing at runtime. Here, we inform the type checkers that 

40# we're importing `typing.cast` as `cast` and re-implement typing.cast's 

41# runtime behavior in a block that is ignored by type checkers. 

42if TYPE_CHECKING: # pragma: no cover 

43 # not executed at runtime 

44 from typing import cast 

45else: 

46 # executed at runtime 

47 def cast(type_, value): # noqa 

48 return value