mirror of https://github.com/pypa/pip
102 lines
3.7 KiB
Python
102 lines
3.7 KiB
Python
"""Utilities to lazily create and visit candidates found.
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Creating and visiting a candidate is a *very* costly operation. It involves
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fetching, extracting, potentially building modules from source, and verifying
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distribution metadata. It is therefore crucial for performance to keep
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everything here lazy all the way down, so we only touch candidates that we
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absolutely need, and not "download the world" when we only need one version of
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something.
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"""
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import functools
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import itertools
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from pip._vendor.six.moves import collections_abc # type: ignore
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from pip._internal.utils.typing import MYPY_CHECK_RUNNING
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if MYPY_CHECK_RUNNING:
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from typing import Callable, Iterator, Optional
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from .base import Candidate
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def _insert_installed(installed, others):
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# type: (Candidate, Iterator[Candidate]) -> Iterator[Candidate]
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"""Iterator for ``FoundCandidates``.
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This iterator is used when the resolver prefers to upgrade an
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already-installed package. Candidates from index are returned in their
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normal ordering, except replaced when the version is already installed.
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The implementation iterates through and yields other candidates, inserting
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the installed candidate exactly once before we start yielding older or
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equivalent candidates, or after all other candidates if they are all newer.
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"""
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installed_yielded = False
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for candidate in others:
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# If the installed candidate is better, yield it first.
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if not installed_yielded and installed.version >= candidate.version:
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yield installed
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installed_yielded = True
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yield candidate
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# If the installed candidate is older than all other candidates.
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if not installed_yielded:
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yield installed
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class FoundCandidates(collections_abc.Sequence):
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"""A lazy sequence to provide candidates to the resolver.
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The intended usage is to return this from `find_matches()` so the resolver
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can iterate through the sequence multiple times, but only access the index
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page when remote packages are actually needed. This improve performances
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when suitable candidates are already installed on disk.
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"""
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def __init__(
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self,
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get_others, # type: Callable[[], Iterator[Candidate]]
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installed, # type: Optional[Candidate]
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prefers_installed, # type: bool
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):
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self._get_others = get_others
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self._installed = installed
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self._prefers_installed = prefers_installed
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def __getitem__(self, index):
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# type: (int) -> Candidate
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# Implemented to satisfy the ABC check. This is not needed by the
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# resolver, and should not be used by the provider either (for
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# performance reasons).
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raise NotImplementedError("don't do this")
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def __iter__(self):
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# type: () -> Iterator[Candidate]
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if not self._installed:
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return self._get_others()
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others = (
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candidate
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for candidate in self._get_others()
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if candidate.version != self._installed.version
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)
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if self._prefers_installed:
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return itertools.chain([self._installed], others)
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return _insert_installed(self._installed, others)
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def __len__(self):
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# type: () -> int
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# Implemented to satisfy the ABC check. This is not needed by the
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# resolver, and should not be used by the provider either (for
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# performance reasons).
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raise NotImplementedError("don't do this")
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@functools.lru_cache(maxsize=1)
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def __bool__(self):
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# type: () -> bool
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if self._prefers_installed and self._installed:
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return True
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return any(self)
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__nonzero__ = __bool__ # XXX: Python 2.
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