Walter Dörwald added the comment:
I'd like to have this feature too. However the code should use
d if d is not None else {}
instead of
d or {}
For example I might want to use a subclass of dict (lowerdict) that converts
all keys to lowercase. When I use an empty lowerdict in new_child(),
new_child() would silently use a normal dict instead:
class lowerdict(dict):
def __getitem__(self, key):
return dict.__getitem__(
self,
key.lower() if isinstance(key, str) else key
)
import collections
cm = collections.ChainMap(lowerdict(), lowerdict())
cm2 = cm.new_child(lowerdict())
print(type(cm2.maps[0]))
This would print <class 'dict'>.
----------
nosy: +doerwalter
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<http://bugs.python.org/issue16613>
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