Mercurial > repos > guerler > springsuite
comparison planemo/lib/python3.7/site-packages/packaging/_typing.py @ 1:56ad4e20f292 draft
"planemo upload commit 6eee67778febed82ddd413c3ca40b3183a3898f1"
| author | guerler |
|---|---|
| date | Fri, 31 Jul 2020 00:32:28 -0400 |
| parents | |
| children |
comparison
equal
deleted
inserted
replaced
| 0:d30785e31577 | 1:56ad4e20f292 |
|---|---|
| 1 """For neatly implementing static typing in packaging. | |
| 2 | |
| 3 `mypy` - the static type analysis tool we use - uses the `typing` module, which | |
| 4 provides core functionality fundamental to mypy's functioning. | |
| 5 | |
| 6 Generally, `typing` would be imported at runtime and used in that fashion - | |
| 7 it acts as a no-op at runtime and does not have any run-time overhead by | |
| 8 design. | |
| 9 | |
| 10 As it turns out, `typing` is not vendorable - it uses separate sources for | |
| 11 Python 2/Python 3. Thus, this codebase can not expect it to be present. | |
| 12 To work around this, mypy allows the typing import to be behind a False-y | |
| 13 optional to prevent it from running at runtime and type-comments can be used | |
| 14 to remove the need for the types to be accessible directly during runtime. | |
| 15 | |
| 16 This module provides the False-y guard in a nicely named fashion so that a | |
| 17 curious maintainer can reach here to read this. | |
| 18 | |
| 19 In 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 | |
| 26 Ref: 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. | |
| 33 if False: # pragma: no cover | |
| 34 from typing import TYPE_CHECKING | |
| 35 else: | |
| 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. | |
| 42 if TYPE_CHECKING: # pragma: no cover | |
| 43 # not executed at runtime | |
| 44 from typing import cast | |
| 45 else: | |
| 46 # executed at runtime | |
| 47 def cast(type_, value): # noqa | |
| 48 return value |