General cleanup. Reverse the class order to allowing pickling to work a bit more natively.

Make the testing a bit smarter to auto skip CFrozenList tests if they don't apply.

Author: csm10495

frozenlist/__init__.py

@@ -13,7 +13,7 @@
 
 
 @total_ordering
-class FrozenList(MutableSequence):
+class PyFrozenList(MutableSequence):
     __slots__ = ("_frozen", "_items")
     __class_getitem__ = classmethod(types.GenericAlias)
 
@@ -92,22 +92,18 @@ def __deepcopy__(self, memo: dict[int, object]):
 
     def __reduce__(self):
         return (
-            _reconstruct_pyfrozenlist,
-            (self._items, self._frozen),
+            self.__class__,
+            (self._items,),
+            {"_frozen": self._frozen},
         )
 
+    def __setstate__(self, state: dict[str, object]):
+        self._frozen = state["_frozen"]
 
-# Store a reference to the pure Python implementation before it's potentially replaced
-PyFrozenList = FrozenList
 
-
-def _reconstruct_pyfrozenlist(items: list[object], frozen: bool) -> PyFrozenList:
-    """Helper function to reconstruct the pure Python FrozenList during unpickling.
-    This function is needed since otherwise the class renaming confuses pickle."""
-    fl = PyFrozenList(items)
-    if frozen:
-        fl.freeze()
-    return fl
+# Rename the pure Python implementation. The C extension (if available) will
+# override this name.
+FrozenList = PyFrozenList
 
 
 if not NO_EXTENSIONS:

frozenlist/_frozenlist.pyx

@@ -127,10 +127,6 @@ cdef class FrozenList:
         cdef FrozenList new_list
         obj_id = id(self)
 
-        # Return existing copy if already processed (circular reference)
-        if obj_id in memo:
-            return memo[obj_id]
-
         # Create new instance and register immediately
         new_list = self.__class__([])
         memo[obj_id] = new_list

tests/test_frozenlist.py

@@ -9,6 +9,13 @@
 
 from frozenlist import FrozenList, PyFrozenList
 
+try:
+    from frozenlist import CFrozenList
+
+    HAS_CFROZENLIST = True
+except ImportError:
+    HAS_CFROZENLIST = False
+
 
 class FrozenListMixin:
     FrozenList = NotImplemented
@@ -414,33 +421,46 @@ def test_picklability_forward_compatible(self, freeze: bool) -> None:
 
         # If this test breaks, we've changed the frozenlist data structure in an incompatible way
         # with previous pickled binaries.
-        if self.FrozenList is FrozenList:
+        if self.FrozenList is PyFrozenList:
             if freeze:
                 assert (
                     pickled
-                    == b"cfrozenlist._frozenlist\nFrozenList\np0\n((lp1\nI1\naI2\natp2\nRp3\n(dp4\nV_frozen\np5\nI01\nsb."
+                    == b"cfrozenlist\nPyFrozenList\np0\n((lp1\nI1\naI2\natp2\nRp3\n(dp4\nV_frozen\np5\nI01\nsb."
                 )
             else:
                 assert (
                     pickled
-                    == b"cfrozenlist._frozenlist\nFrozenList\np0\n((lp1\nI1\naI2\natp2\nRp3\n(dp4\nV_frozen\np5\nI00\nsb."
+                    == b"cfrozenlist\nPyFrozenList\np0\n((lp1\nI1\naI2\natp2\nRp3\n(dp4\nV_frozen\np5\nI00\nsb."
                 )
-        elif self.FrozenList is PyFrozenList:
+        elif self.FrozenList is FrozenList:
             if freeze:
                 assert (
                     pickled
-                    == b"cfrozenlist\n_reconstruct_pyfrozenlist\np0\n((lp1\nI1\naI2\naI01\ntp2\nRp3\n."
+                    == b"cfrozenlist._frozenlist\nFrozenList\np0\n((lp1\nI1\naI2\natp2\nRp3\n(dp4\nV_frozen\np5\nI01\nsb."
                 )
             else:
                 assert (
                     pickled
-                    == b"cfrozenlist\n_reconstruct_pyfrozenlist\np0\n((lp1\nI1\naI2\naI00\ntp2\nRp3\n."
+                    == b"cfrozenlist._frozenlist\nFrozenList\np0\n((lp1\nI1\naI2\natp2\nRp3\n(dp4\nV_frozen\np5\nI00\nsb."
                 )
+        else:
+            pytest.fail("Unknown FrozenList implementation.")
 
 
-class TestFrozenList(FrozenListMixin):
-    FrozenList = FrozenList  # type: ignore[assignment]  # FIXME
+if HAS_CFROZENLIST:
+    # If we don't have CFrozenList, skip adding the test class specifically for it.
+    class TestFrozenList(FrozenListMixin):
+        FrozenList = CFrozenList  # type: ignore[assignment]  # FIXME
 
 
 class TestFrozenListPy(FrozenListMixin):
+    # All implementations will at least have the Python version.
     FrozenList = PyFrozenList  # type: ignore[assignment]  # FIXME
+
+
+def test_frozenlist_aliasing() -> None:
+    """Test that FrozenList name points to the C extension if available, else to PyFrozenList."""
+    if HAS_CFROZENLIST:
+        assert FrozenList is CFrozenList
+    else:
+        assert FrozenList is PyFrozenList