Make sure that frozenlists are pickle-able

Add contributors / changes updates

Add missing file

Author: csm10495

CHANGES/650.contrib

@@ -1,3 +1,2 @@
-The pull request template to be consistent with :ref:`the contributing guidelines
-<adding change notes with your prs>`, particularly the list of categories
+The pull request template to be consistent with :ref:`the contributing guidelines <adding change notes with your prs>`, particularly the list of categories
 -- by :user:`musicinmybrain`.

CHANGES/718.bugfix.rst

@@ -0,0 +1,2 @@
+Fix bug where FrozenList could not be pickled/unpickled.
+-- by :user:`csm10495`.

CONTRIBUTORS.txt

@@ -1,6 +1,7 @@
 - Contributors -
 ----------------
 Andrew Svetlov
+Charles Machalow
 Edgar Ramírez-Mondragón
 Marcin Konowalczyk
 Martijn Pieters

docs/spelling_wordlist.txt

@@ -302,6 +302,7 @@ unicode
 unittest
 Unittest
 unix
+unpickled
 unsets
 unstripped
 upstr

frozenlist/__init__.py

@@ -1,11 +1,17 @@
+import copy
 import os
 import types
 from collections.abc import MutableSequence
 from functools import total_ordering
+from typing import Any
 
 __version__ = "1.8.1.dev0"
 
-__all__ = ("FrozenList", "PyFrozenList")  # type: Tuple[str, ...]
+__all__ = (
+    "FrozenList",
+    "PyFrozenList",
+    "_reconstruct_pyfrozenlist",
+)  # type: Tuple[str, ...]
 
 
 NO_EXTENSIONS = bool(os.environ.get("FROZENLIST_NO_EXTENSIONS"))  # type: bool
@@ -73,7 +79,43 @@ def __hash__(self):
         else:
             raise RuntimeError("Cannot hash unfrozen list.")
 
+    def __deepcopy__(self, memo: dict[int, Any]):
+        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
+
+        # Deep copy items
+        new_list._items[:] = [copy.deepcopy(item, memo) for item in self._items]
+
+        # Preserve frozen state
+        if self._frozen:
+            new_list.freeze()
+
+        return new_list
+
+    def __reduce__(self):
+        return (
+            _reconstruct_pyfrozenlist,
+            (self._items, self._frozen),
+        )
+
+
+def _reconstruct_pyfrozenlist(items, frozen):
+    """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
+
+
+# Store a reference to the pure Python implementation before it's potentially replaced
 PyFrozenList = FrozenList
 
 

frozenlist/_frozenlist.pyx

@@ -144,5 +144,15 @@ cdef class FrozenList:
 
         return new_list
 
+    def __reduce__(self):
+        return (
+            self.__class__,
+            (self._items,),
+            {"_frozen": self._frozen.load()},
+        )
+
+    def __setstate__(self, state):
+        self._frozen.store(state["_frozen"])
+
 
 MutableSequence.register(FrozenList)

tests/test_frozenlist.py

@@ -1,6 +1,7 @@
 # FIXME:
 # mypy: disable-error-code="misc"
 
+import pickle
 from collections.abc import MutableSequence
 from copy import deepcopy
 
@@ -372,6 +373,23 @@ def test_deepcopy_multiple_references(self) -> None:
         assert len(copied[1]) == 3  # Should see the change
         assert len(shared) == 2  # Original unchanged
 
+    @pytest.mark.parametrize("freeze", [True, False])
+    def test_picklability(self, freeze: bool) -> None:
+        # Test that the list can be pickled and unpickled successfully
+        orig = self.FrozenList([1, 2, 3])
+        if freeze:
+            orig.freeze()
+
+        assert orig.frozen == freeze
+
+        pickled = pickle.dumps(orig)
+        unpickled = pickle.loads(pickled)
+        assert unpickled == orig
+        assert unpickled is not orig
+        assert list(unpickled) == list(orig)
+
+        assert unpickled.frozen == freeze
+
 
 class TestFrozenList(FrozenListMixin):
     FrozenList = FrozenList  # type: ignore[assignment]  # FIXME