[New-bugs-announce] [issue35540] dataclasses.asdict breaks with defaultdict fields
Will T
report at bugs.python.org
Wed Dec 19 17:06:44 EST 2018
New submission from Will T <timwilloney at gmail.com>:
_asdict_inner attempts to manually recursively deepcopy dicts by calling type(obj) with a generator of transformed keyvalue tuples @ https://github.com/python/cpython/blob/b2f642ccd2f65d2f3bf77bbaa103dd2bc2733734/Lib/dataclasses.py#L1080 . defaultdicts are dicts so this runs but unlike other dicts their first arg has to be a callable or None:
import collections
import dataclasses as dc
@dc.dataclass()
class C:
d: dict
c = C(collections.defaultdict(lambda: 3, {}))
d = dc.asdict(c)
assert isinstance(d['d'], collections.defaultdict)
assert d['d']['a'] == 3
=>
Traceback (most recent call last):
File "boom.py", line 9, in <module>
d = dc.asdict(c)
File "/Users/spinlock/.pyenv/versions/3.7.1/lib/python3.7/dataclasses.py", line 1019, in asdict
return _asdict_inner(obj, dict_factory)
File "/Users/spinlock/.pyenv/versions/3.7.1/lib/python3.7/dataclasses.py", line 1026, in _asdict_inner
value = _asdict_inner(getattr(obj, f.name), dict_factory)
File "/Users/spinlock/.pyenv/versions/3.7.1/lib/python3.7/dataclasses.py", line 1058, in _asdict_inner
for k, v in obj.items())
TypeError: first argument must be callable or None
I understand that it isn't this bit of code's job to support every dict (and list etc.) subclass under the sun but given defaultdict is stdlib it's imo worth supporting explicitly.
----------
components: Library (Lib)
messages: 332166
nosy: wrmsr
priority: normal
severity: normal
status: open
title: dataclasses.asdict breaks with defaultdict fields
versions: Python 3.7
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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue35540>
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