defaultdict setdefault method not using the default_factory initializer parameter

[MarcoPeli]

Bug report

Bug description:

test = defaultdict(set) #sets default factory method
test['ok'].add(1) # this is ok
test.setdefault('not_ok') # this should use the default factory method, dry principle
test['not_ok'].add(1) # error here, NoneType doesn't have add method :(

_ = test['ok2'] # this is a workaround to add a key using default factory

CPython versions tested on:

3.12

Operating systems tested on:

Windows

[zware]

The setdefault method is just inherited from the base dict type. Its signature is (key, default=None, /); if key does not already exist in the dict/defaultdict, its value is set to default, which defaults to None and the value stored in the dict at key is returned. I'm afraid its very unlikely that setdefault will be changed on defaultdict, as it would be a significant backwards-incompatible change.

Note that your workaround example does not require the _ = part; just test['ok2'] is enough to populate the 'ok2' key.