Skip to content

bpo-43999: If using a frozen class with slots, add __getstate__ and __setstate__ #25786

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Merged
ericvsmith merged 1 commit into from
May 1, 2021
Merged

bpo-43999: If using a frozen class with slots, add __getstate__ and __setstate__ #25786

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
23 changes: 21 additions & 2 deletions Lib/dataclasses.py
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -1087,14 +1087,28 @@ def _process_class(cls, init, repr, eq, order, unsafe_hash, frozen,
tuple(f.name for f in std_init_fields))

if slots:
cls = _add_slots(cls)
cls = _add_slots(cls, frozen)

abc.update_abstractmethods(cls)

return cls


def _add_slots(cls):
# _dataclass_getstate and _dataclass_setstate are needed for pickling frozen
# classes with slots. These could be slighly more performant if we generated
# the code instead of iterating over fields. But that can be a project for
# another day, if performance becomes an issue.
def _dataclass_getstate(self):
return [getattr(self, f.name) for f in fields(self)]


def _dataclass_setstate(self, state):
for field, value in zip(fields(self), state):
# use setattr because dataclass may be frozen
object.__setattr__(self, field.name, value)


def _add_slots(cls, is_frozen):
# Need to create a new class, since we can't set __slots__
# after a class has been created.

Expand All @@ -1120,6 +1134,11 @@ def _add_slots(cls):
if qualname is not None:
cls.__qualname__ = qualname

if is_frozen:
# Need this for pickling frozen classes with slots.
cls.__getstate__ = _dataclass_getstate
cls.__setstate__ = _dataclass_setstate

return cls


Expand Down
13 changes: 13 additions & 0 deletions Lib/test/test_dataclasses.py
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -2833,6 +2833,19 @@ class A:
self.assertFalse(hasattr(A, "__slots__"))
self.assertTrue(hasattr(B, "__slots__"))

# Can't be local to test_frozen_pickle.
@dataclass(frozen=True, slots=True)
class FrozenSlotsClass:
foo: str
bar: int

def test_frozen_pickle(self):
# bpo-43999

assert self.FrozenSlotsClass.__slots__ == ("foo", "bar")
p = pickle.dumps(self.FrozenSlotsClass("a", 1))
assert pickle.loads(p) == self.FrozenSlotsClass("a", 1)


class TestDescriptors(unittest.TestCase):
def test_set_name(self):
Expand Down