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- """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
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