Bug in ChainMap if one of the items is empty defaultdict

Bug report

Bug description:

from collections import defaultdict, ChainMap
a = ChainMap({1: {2: "a"}}, defaultdict(dict), {3: {4 : "b"}})
print(dict(a))
# Output: {3: {}, 1: {2: 'a'}}
# Expected Output: {3: {4: 'b'}, 1: {2: 'a'}}

CPython versions tested on:

3.11

Operating systems tested on:

Linux

You're not using ChainMap and there is no output and you're doing the same thing twice...

I'm think the example was meant to look something like this:

>>> a = ChainMap({1: {2: "a"}}, defaultdict(dict), {3: {4 : "b"}})
>>> a[3]
{}
>>> a
ChainMap({1: {2: 'a'}}, defaultdict(<class 'dict'>, {3: {}}), {3: {4: 'b'}})

If that is the case, then this isn't a bug. A defaultdict always shadows downstream mappings because is was specifically designed to always return some value whether or not a key is present.

Thanks for clarifying. When I was converting ChainMap to dict, it was overriding the latest value for key 3.

Since this doesn't seem to be a bug, I'm going to close this.

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Bug in ChainMap if one of the items is empty defaultdict #117576

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Bug in ChainMap if one of the items is empty defaultdict #117576

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Bug report

Bug description:

CPython versions tested on:

Operating systems tested on:

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pochmann3 commented on Apr 6, 2024

rhettinger commented on Apr 6, 2024

erastogi commented on Apr 11, 2024

ericvsmith commented on Apr 14, 2024

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