Steven D'Aprano <steve+pyt...@pearwood.info> added the comment:
As Larry said, yes, this is expected behaviour, and has nothing to do with the
for loop. The purpose of defaultdict is that dict lookups create the entry if
it doesn't exist:
>>> from collections import defaultdict
>>> d = defaultdict(list)
>>> x = d['any key']
>>> d
defaultdict(<class 'list'>, {'any key': []})
So even though your code loops zero times, you have created a key 'a' with
value [].
----------
nosy: +steven.daprano
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Python tracker <rep...@bugs.python.org>
<https://bugs.python.org/issue42310>
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