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Lazy-evaluate candidates with installed inserted
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uranusjr committed Dec 15, 2020
1 parent c1dc7a8 commit 93ec9a2
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Showing 2 changed files with 18 additions and 12 deletions.
2 changes: 2 additions & 0 deletions news/9284.bugfix.rst
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New resolver: Always iterate through candidates from indexes lazily to avoid
downloading candidates we do not need.
28 changes: 16 additions & 12 deletions src/pip/_internal/resolution/resolvelib/found_candidates.py
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import itertools
import operator

from pip._vendor.six.moves import collections_abc # type: ignore

Expand Down Expand Up @@ -32,18 +31,23 @@ def _insert_installed(installed, others):
already-installed package. Candidates from index are returned in their
normal ordering, except replaced when the version is already installed.
Since candidates from index are already sorted by reverse version order,
`sorted()` here would keep the ordering mostly intact, only shuffling the
already-installed candidate into the correct position. We put the already-
installed candidate in front of those from the index, so it's put in front
after sorting due to Python sorting's stableness guarentee.
The implementation iterates through and yields other candidates, but insert
the installed candidate exactly once before we start yielding older or
equivalent candidates, or after all other candidates if they are all newer.
"""
candidates = sorted(
itertools.chain([installed], others),
key=operator.attrgetter("version"),
reverse=True,
)
return iter(candidates)
installed_yielded = False

for candidate in others:
# If the installed candidate if better, yield it first.
if not installed_yielded and installed.version >= candidate.version:
yield installed
installed_yielded = True

yield candidate

# If the installed candidate is older than all other candidates.
if not installed_yielded:
yield installed


class FoundCandidates(collections_abc.Sequence):
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