Merge pull request #10261 from jdufresne/found-candidates-six

Remove six import in resolution/resolvelib/found_candidates.py

Author: uranusjr

news/69311721-677c-46c7-9f29-31a40dddee99.trivial.rst

@@ -9,15 +9,30 @@
 """
 
 import functools
-from typing import Callable, Iterator, Optional, Set, Tuple
+from collections.abc import Sequence
+from typing import TYPE_CHECKING, Any, Callable, Iterator, Optional, Set, Tuple
 
 from pip._vendor.packaging.version import _BaseVersion
-from pip._vendor.six.moves import collections_abc  # type: ignore
 
 from .base import Candidate
 
 IndexCandidateInfo = Tuple[_BaseVersion, Callable[[], Optional[Candidate]]]
 
+if TYPE_CHECKING:
+    SequenceCandidate = Sequence[Candidate]
+else:
+    # For compatibility: Python before 3.9 does not support using [] on the
+    # Sequence class.
+    #
+    # >>> from collections.abc import Sequence
+    # >>> Sequence[str]
+    # Traceback (most recent call last):
+    #   File "<stdin>", line 1, in <module>
+    # TypeError: 'ABCMeta' object is not subscriptable
+    #
+    # TODO: Remove this block after dropping Python 3.8 support.
+    SequenceCandidate = Sequence
+
 
 def _iter_built(infos: Iterator[IndexCandidateInfo]) -> Iterator[Candidate]:
     """Iterator for ``FoundCandidates``.
@@ -90,7 +105,7 @@ def _iter_built_with_inserted(
         yield installed
 
 
-class FoundCandidates(collections_abc.Sequence):
+class FoundCandidates(SequenceCandidate):
     """A lazy sequence to provide candidates to the resolver.
 
     The intended usage is to return this from `find_matches()` so the resolver
@@ -111,7 +126,7 @@ def __init__(
         self._prefers_installed = prefers_installed
         self._incompatible_ids = incompatible_ids
 
-    def __getitem__(self, index: int) -> Candidate:
+    def __getitem__(self, index: Any) -> Any:
         # Implemented to satisfy the ABC check. This is not needed by the
         # resolver, and should not be used by the provider either (for
         # performance reasons).