[New-bugs-announce] [issue43999] Cannot pickle frozen dataclasses with slots

Eric V. Smith report at bugs.python.org
Sat May 1 12:03:38 EDT 2021

New submission from Eric V. Smith <eric at trueblade.com>:

Originally reported in https://github.com/ericvsmith/dataclasses/issues/154

import pickle
from dataclasses import dataclass

@dataclass(frozen=True, slots=True)
class ExampleDataclass:
    foo: str
    bar: int

assert ExampleDataclass.__slots__ == ("foo", "bar")

assert pickle.loads(
    pickle.dumps(ExampleDataclass("a", 1))
) == ExampleDataclass("a", 1)

  File "<string>", line 4, in __setattr__
dataclasses.FrozenInstanceError: cannot assign to field 'foo'

I'll get a PR ready, likely based on ariebovenberg's solution in the above mentioned issue.

assignee: eric.smith
components: Library (Lib)
messages: 392603
nosy: eric.smith
priority: deferred blocker
severity: normal
status: open
title: Cannot pickle frozen dataclasses with slots
versions: Python 3.10

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