| """For neatly implementing static typing in pip. |
| |
| `mypy` - the static type analysis tool we use - uses the `typing` module, which |
| provides core functionality fundamental to mypy's functioning. |
| |
| Generally, `typing` would be imported at runtime and used in that fashion - |
| it acts as a no-op at runtime and does not have any run-time overhead by |
| design. |
| |
| As it turns out, `typing` is not vendorable - it uses separate sources for |
| Python 2/Python 3. Thus, this codebase can not expect it to be present. |
| To work around this, mypy allows the typing import to be behind a False-y |
| optional to prevent it from running at runtime and type-comments can be used |
| to remove the need for the types to be accessible directly during runtime. |
| |
| This module provides the False-y guard in a nicely named fashion so that a |
| curious maintainer can reach here to read this. |
| |
| In pip, all static-typing related imports should be guarded as follows: |
| |
| from pip._internal.utils.typing import MYPY_CHECK_RUNNING |
| |
| if MYPY_CHECK_RUNNING: |
| from typing import ... |
| |
| Ref: https://github.com/python/mypy/issues/3216 |
| """ |
| |
| MYPY_CHECK_RUNNING = False |
| |
| |
| if MYPY_CHECK_RUNNING: |
| from typing import cast |
| else: |
| # typing's cast() is needed at runtime, but we don't want to import typing. |
| # Thus, we use a dummy no-op version, which we tell mypy to ignore. |
| def cast(type_, value): # type: ignore |
| return value |
