perf: skip hash property (#1115)

Author: notatallshaw

benchmarks/version.py

@@ -41,6 +41,11 @@ def time_hash(self) -> None:
         for v in self.valid_versions:
             hash(Version(v))
 
+    @add_attributes(pretty_name="Version hash (warm cache)")
+    def time_hash_warm(self) -> None:
+        for v in self.version_objects_warm:
+            hash(v)
+
     @add_attributes(pretty_name="Version __str__")
     def time_str(self) -> None:
         for version in self.valid_versions:

src/packaging/version.py

@@ -551,7 +551,16 @@ def _key(self) -> CmpKey:
     # __hash__ must be defined when __eq__ is overridden,
     # otherwise Python sets __hash__ to None.
     def __hash__(self) -> int:
-        return hash(self._key)
+        if self._key_cache is None:
+            self._key_cache = _cmpkey(
+                self._epoch,
+                self._release,
+                self._pre,
+                self._post,
+                self._dev,
+                self._local,
+            )
+        return hash(self._key_cache)
 
     # Override comparison methods to use direct _key_cache access
     # This is faster than property access, especially before Python 3.12