What this snippet does
Mutations in a ChainMap only affect the first dictionary in the chain, not the one where the key was found.
Expected output
{'b': 2}Why practise typing this
Typing standard library (collections) code builds muscle memory for the symbols and indentation Python uses most, which prose-based typing tests never cover. DevType measures your words per minute and accuracy on this snippet and tracks the individual characters you mistype, so later lessons can target them.
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