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But one should be cautious while using ChainMap there's a catch that if you have duplicate keys the values from first mapping get used and when you call a del on say a ChainMap c will delete the first mapping of that key.
– Slayer
Commented Feb 14, 2017 at 5:14
13

@Prerit What else would you expect it to do? That's the normal way chained namespaces work. Consider how $PATH works in bash. Deleting an executable on the path doesn't preclude another executable with the same name further upstream.
– Raymond Hettinger
Commented Feb 15, 2017 at 7:24
4

@Raymond Hettinger I agree, just added a caution. Most people may not know about it. :D
– Slayer
Commented Feb 15, 2017 at 15:15
@Prerit You could cast to dict to avoid that, i.e.: dict(ChainMap({}, y, x))
– wjandrea
Commented Jul 15, 2019 at 16:30
@RaymondHettinger We all know you designed ChainMap in the most reasonable way, thank you for it!
– run_the_race
Commented May 29, 2022 at 18:16

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