python中ChainMap如何实例化

>>> from collections import ChainMap

>>> from collections import OrderedDict, defaultdict

>>> # Use no arguments

>>> ChainMap()

ChainMap({})

>>> # Use regular dictionaries

>>> numbers = {"one": 1, "two": 2}

>>> letters = {"a": "A", "b": "B"}

>>> ChainMap(numbers, letters)

ChainMap({'one': 1, 'two': 2}, {'a': 'A', 'b': 'B'})

>>> ChainMap(numbers, {"a": "A", "b": "B"})

ChainMap({'one': 1, 'two': 2}, {'a': 'A', 'b': 'B'})

>>> # Use other mappings

>>> numbers = OrderedDict(one=1, two=2)

>>> letters = defaultdict(str, {"a": "A", "b": "B"})

>>> ChainMap(numbers, letters)

ChainMap(

    OrderedDict([('one', 1), ('two', 2)]),

    defaultdict(<class 'str'>, {'a': 'A', 'b': 'B'})

)