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import sys
import platform
__all__ = ['install', 'NullFinder', 'Protocol']
try:
from typing import Protocol
except ImportError: # pragma: no cover
from ..typing_extensions import Protocol # type: ignore
def install(cls):
"""
Class decorator for installation on sys.meta_path.
Adds the backport DistributionFinder to sys.meta_path and
attempts to disable the finder functionality of the stdlib
DistributionFinder.
"""
sys.meta_path.append(cls())
disable_stdlib_finder()
return cls
def disable_stdlib_finder():
"""
Give the backport primacy for discovering path-based distributions
by monkey-patching the stdlib O_O.
See #91 for more background for rationale on this sketchy
behavior.
"""
def matches(finder):
return getattr(
finder, '__module__', None
) == '_frozen_importlib_external' and hasattr(finder, 'find_distributions')
for finder in filter(matches, sys.meta_path): # pragma: nocover
del finder.find_distributions
class NullFinder:
"""
A "Finder" (aka "MetaClassFinder") that never finds any modules,
but may find distributions.
"""
@staticmethod
def find_spec(*args, **kwargs):
return None
# In Python 2, the import system requires finders
# to have a find_module() method, but this usage
# is deprecated in Python 3 in favor of find_spec().
# For the purposes of this finder (i.e. being present
# on sys.meta_path but having no other import
# system functionality), the two methods are identical.
find_module = find_spec
def pypy_partial(val):
"""
Adjust for variable stacklevel on partial under PyPy.
Workaround for #327.
"""
is_pypy = platform.python_implementation() == 'PyPy'
return val + is_pypy
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