Merge pull request #13660 from notatallshaw/assume-packaging-Versions-on-python-3.11+

Don't convert versions to strings when using importlib.metadata backend

Author: notatallshaw

news/13660.feature.rst

@@ -0,0 +1,2 @@
+When using the ``importlib.metadata`` backend, pip skips redundant work
+converting version objects to strings and back to version objects.

src/pip/_internal/index/package_finder.py

@@ -18,7 +18,7 @@
 from pip._vendor.packaging import specifiers
 from pip._vendor.packaging.tags import Tag
 from pip._vendor.packaging.utils import NormalizedName, canonicalize_name
-from pip._vendor.packaging.version import InvalidVersion, _BaseVersion
+from pip._vendor.packaging.version import InvalidVersion, Version, _BaseVersion
 from pip._vendor.packaging.version import parse as parse_version
 
 from pip._internal.exceptions import (
@@ -28,6 +28,7 @@
     UnsupportedWheel,
 )
 from pip._internal.index.collector import LinkCollector, parse_links
+from pip._internal.metadata import select_backend
 from pip._internal.models.candidate import InstallationCandidate
 from pip._internal.models.format_control import FormatControl
 from pip._internal.models.link import Link
@@ -458,14 +459,19 @@ def get_applicable_candidates(
         allow_prereleases = self._allow_all_prereleases or None
         specifier = self._specifier
 
-        # We turn the version object into a str here because otherwise
-        # when we're debundled but setuptools isn't, Python will see
-        # packaging.version.Version and
+        # When using the pkg_resources backend we turn the version object into
+        # a str here because otherwise when we're debundled but setuptools isn't,
+        # Python will see packaging.version.Version and
         # pkg_resources._vendor.packaging.version.Version as different
         # types. This way we'll use a str as a common data interchange
         # format. If we stop using the pkg_resources provided specifier
         # and start using our own, we can drop the cast to str().
-        candidates_and_versions = [(c, str(c.version)) for c in candidates]
+        if select_backend().NAME == "pkg_resources":
+            candidates_and_versions: list[
+                tuple[InstallationCandidate, str | Version]
+            ] = [(c, str(c.version)) for c in candidates]
+        else:
+            candidates_and_versions = [(c, c.version) for c in candidates]
         versions = set(
             specifier.filter(
                 (v for _, v in candidates_and_versions),