追加到列表的字典可为每个键增加价值 [英] Appending to dict of lists adds value to every key

问题描述

我有一个空列表的字典，所有键都在开头声明:

I have a dictionary of empty lists with all keys declared at the beginning:

>>> keys = ["k1", "k2", "k3"]
>>> d = dict.fromkeys(keys, [])
>>> d
{'k2': [], 'k3': [], 'k1': []}

当我尝试将一个坐标对(列表 ["x1"，"y1"] )添加到键的一个列表中时，它会添加到所有键的列表中:

When I try to add a coordinate pair (the list ["x1", "y1"]) to one of the key's lists, it instead adds to all the keys' lists:

>>> d["k1"].append(["x1", "y1"])
>>> d
{'k1': [['x1', 'y1']], 'k2': [['x1', 'y1']], 'k3': [['x1', 'y1']]}

我要找的是:

>>> d
{'k1': [['x1', 'y1']], 'k3': [], 'k1': []}

如何在Python 3中实现这一目标?

How can I achieve this in Python 3?

推荐答案

看起来每个列表实际上都是对单个列表的引用.附加其中之一会附加所有这些.

Looks like each of those lists is actually a reference to a single list. Appending to one of them appends to all of them.

我认为您仍然可以使用 fromkeys 来解决此问题.尝试改用dict理解.

I don't think you can work around this while still using fromkeys. Try using a dict comprehension instead.

d = {k: [] for k in keys}

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