pylock support for Python pre-releases (#1179)

Author: sbidoul

src/packaging/markers.py

@@ -484,6 +484,16 @@ def evaluate(
         )
 
 
+def _pep440_python_full_version(python_full_version: str) -> str:
+    """
+    Work around platform.python_version() returning something that is not PEP 440
+    compliant for non-tagged Python builds.
+    """
+    if python_full_version.endswith("+"):
+        return f"{python_full_version}local"
+    return python_full_version
+
+
 def _repair_python_full_version(
     env: dict[str, str | AbstractSet[str]],
 ) -> dict[str, str | AbstractSet[str]]:
@@ -492,6 +502,5 @@ def _repair_python_full_version(
     compliant for non-tagged Python builds.
     """
     python_full_version = cast("str", env["python_full_version"])
-    if python_full_version.endswith("+"):
-        env["python_full_version"] = f"{python_full_version}local"
+    env["python_full_version"] = _pep440_python_full_version(python_full_version)
     return env

src/packaging/pylock.py

@@ -16,7 +16,12 @@
 )
 from urllib.parse import urlparse
 
-from .markers import Environment, Marker, default_environment
+from .markers import (
+    Environment,
+    Marker,
+    _pep440_python_full_version,
+    default_environment,
+)
 from .specifiers import SpecifierSet
 from .tags import create_compatible_tags_selector, sys_tags
 from .utils import (
@@ -782,7 +787,7 @@ def select(
                 ),
             ),
         )
-        env_python_full_version = (
+        env_python_full_version = _pep440_python_full_version(
             environment["python_full_version"]
             if environment
             else default_environment()["python_full_version"]

tests/test_pylock_select.py

@@ -7,7 +7,7 @@
 
 import pytest
 
-from packaging.markers import Marker
+from packaging.markers import Marker, default_environment
 from packaging.pylock import (
     Package,
     PackageArchive,
@@ -369,3 +369,24 @@ def test_extras_and_groups(
         )
     ]
     assert selected_names == expected
+
+
+def test_python_prerelease() -> None:
+    """Python pre-release versions are not PEP 440 compliant.
+    Test that Pylock.requires_python supports that.
+    """
+    pylock = Pylock(
+        lock_version=Version("1.0"),
+        created_by="repro",
+        requires_python=SpecifierSet(">=3.12"),
+        packages=[
+            Package(
+                name=cast("NormalizedName", "pkga"),
+                requires_python=SpecifierSet(">=3.12"),
+                directory=PackageDirectory(path="./pkga"),
+            )
+        ],
+    )
+    env = default_environment()
+    env["python_full_version"] = "3.15.0a8+"
+    list(pylock.select(environment=env))