[issue32792] ChainMap should preserve order of underlying mappings

[Serhiy Storchaka]

Serhiy Storchaka <storchaka+cpython at gmail.com> added the comment:

Sorry, I was wrong. reversed() is not needed here.

The advantage of this implementation is that it can be faster because of iterating mappings in C code instead of Python code. But the side effect of it is that the iterator keeps references to all values. If this is not desirable, the code can be written something like:

    return iter(dict.fromkeys(itertools.chain.from_iterable(self.maps)))

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<https://bugs.python.org/issue32792>
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