bpo-36060: Document how collections.ChainMap() determines iteration o… · python/cpython@7121a6e (original) (raw)
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``` :func:super function. A reference to d.parents is equivalent to:
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``` ``ChainMap(*d.maps[1:])``.
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Note, the iteration order of a :class:ChainMap() is determined by
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scanning the mappings last to first::
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baseline = {'music': 'bach', 'art': 'rembrandt'}
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adjustments = {'art': 'van gogh', 'opera': 'carmen'}
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list(ChainMap(adjustments, baseline))
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['music', 'art', 'opera']
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This gives the same ordering as a series of :meth:dict.update calls
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starting with the last mapping::
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combined = baseline.copy()
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combined.update(adjustments)
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list(combined)
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['music', 'art', 'opera']
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`.. seealso::
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