Mercurial > repos > shellac > sam_consensus_v3
diff env/lib/python3.9/site-packages/pkg_resources/_vendor/packaging/_typing.py @ 0:4f3585e2f14b draft default tip
"planemo upload commit 60cee0fc7c0cda8592644e1aad72851dec82c959"
author | shellac |
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date | Mon, 22 Mar 2021 18:12:50 +0000 |
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--- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/env/lib/python3.9/site-packages/pkg_resources/_vendor/packaging/_typing.py Mon Mar 22 18:12:50 2021 +0000 @@ -0,0 +1,48 @@ +"""For neatly implementing static typing in packaging. + +`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 packaging, all static-typing related imports should be guarded as follows: + + from packaging._typing import TYPE_CHECKING + + if TYPE_CHECKING: + from typing import ... + +Ref: https://github.com/python/mypy/issues/3216 +""" + +__all__ = ["TYPE_CHECKING", "cast"] + +# The TYPE_CHECKING constant defined by the typing module is False at runtime +# but True while type checking. +if False: # pragma: no cover + from typing import TYPE_CHECKING +else: + TYPE_CHECKING = False + +# typing's cast syntax requires calling typing.cast at runtime, but we don't +# want to import typing at runtime. Here, we inform the type checkers that +# we're importing `typing.cast` as `cast` and re-implement typing.cast's +# runtime behavior in a block that is ignored by type checkers. +if TYPE_CHECKING: # pragma: no cover + # not executed at runtime + from typing import cast +else: + # executed at runtime + def cast(type_, value): # noqa + return value