python中ChainMap突变怎么用

这篇文章主要介绍python中ChainMap突变怎么用，文中介绍的非常详细，具有一定的参考价值，感兴趣的小伙伴们一定要看完！

1、ChainMap支持突变。换句话说，允许更新、添加、删除和弹出键。这种情况这些操作只作用于第一个映射。

>>> from collections import ChainMap >>> numbers = {"one": 1, "two": 2}>>> letters = {"a": "A", "b": "B"} >>> alpha_num = ChainMap(numbers, letters)>>> alpha_numChainMap({'one': 1, 'two': 2}, {'a': 'A', 'b': 'B'}) >>> # Add a new key-value pair>>> alpha_num["c"] = "C">>> alpha_numChainMap({'one': 1, 'two': 2, 'c': 'C'}, {'a': 'A', 'b': 'B'}) >>> # Update an existing key>>> alpha_num["b"] = "b">>> alpha_numChainMap({'one': 1, 'two': 2, 'c': 'C', 'b': 'b'}, {'a': 'A', 'b': 'B'}) >>> # Pop keys>>> alpha_num.pop("two")2>>> alpha_num.pop("a")Traceback (most recent call last):    ...KeyError: "Key not found in the first mapping: 'a'" >>> # Delete keys>>> del alpha_num["c"]>>> alpha_numChainMap({'one': 1, 'b': 'b'}, {'a': 'A', 'b': 'B'})>>> del alpha_num["a"]Traceback (most recent call last):    ...KeyError: "Key not found in the first mapping: 'a'" >>> # Clear the dictionary>>> alpha_num.clear()>>> alpha_numChainMap({}, {'a': 'A', 'b': 'B'})

2、改变给定链映射内容的操作只会影响第一个映射，即使试图改变列表中的其他映射中的键。

可以使用此行为创建可更新的链映射，而不修改原始输入字典。在这种情况下，您可以使用空字典作为ChainMap的第一个参数。

>>> from collections import ChainMap >>> numbers = {"one": 1, "two": 2}>>> letters = {"a": "A", "b": "B"} >>> alpha_num = ChainMap({}, numbers, letters)>>> alpha_numChainMap({}, {'one': 1, 'two': 2}, {'a': 'A', 'b': 'B'}) >>> alpha_num["comma"] = ",">>> alpha_num["period"] = "." >>> alpha_numChainMap(    {'comma': ',', 'period': '.'},    {'one': 1, 'two': 2},    {'a': 'A', 'b': 'B'})

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