allow prerelease versions in marker evaluation (#523)

Fixes  #522

Author: graingert

packaging/markers.py

@@ -192,7 +192,7 @@ def _eval_op(lhs: str, op: Op, rhs: str) -> bool:
     except InvalidSpecifier:
         pass
     else:
-        return spec.contains(lhs)
+        return spec.contains(lhs, prereleases=True)
 
     oper: Optional[Operator] = _operators.get(op.serialize())
     if oper is None:

tests/test_markers.py

@@ -86,6 +86,11 @@ def test_fails_when_undefined(self):
         with pytest.raises(UndefinedComparison):
             Marker("'2.7.0' ~= os_name").evaluate()
 
+    def test_allows_prerelease(self):
+        assert Marker('python_full_version > "3.6.2"').evaluate(
+            {"python_full_version": "3.11.0a5"}
+        )
+
 
 FakeVersionInfo = collections.namedtuple(
     "FakeVersionInfo", ["major", "minor", "micro", "releaselevel", "serial"]