从Python字典中删除项目的最佳方式？ [英] Best way to remove an item from a Python dictionary?

问题描述

当项目的键未知时，从字典中删除项目的最佳方式是什么？这是一个简单的方法：

What is the best way to remove an item from a dictionary when the item's key is unknown? Here's a simple approach:

for key, item in some_dict.items():
    if item is item_to_remove:
        del some_dict[key]

有更好的方法吗？

推荐答案

请注意，您正在测试对于对象身份（是只返回 True 如果两个操作数都由内存中的同一个对象表示 - 这并不总是两个对象的情况与 == 相比较）。如果您有意这样做，那么您可以将代码重写为

Be aware that you're currently testing for object identity (is only returns True if both operands are represented by the same object in memory - this is not always the case with two object that compare equal with ==). If you are doing this on purpose, then you could rewrite your code as

some_dict = {key: value for key, value in some_dict.items() 
             if value is not value_to_remove}

但这可能不会做什么你想要：

But this may not do what you want:

>>> some_dict = {1: "Hello", 2: "Goodbye", 3: "You say yes", 4: "I say no"}
>>> value_to_remove = "You say yes"
>>> some_dict = {key: value for key, value in some_dict.items() if value is not value_to_remove}
>>> some_dict
{1: 'Hello', 2: 'Goodbye', 3: 'You say yes', 4: 'I say no'}
>>> some_dict = {key: value for key, value in some_dict.items() if value != value_to_remove}
>>> some_dict
{1: 'Hello', 2: 'Goodbye', 4: 'I say no'}

所以你可能想要！= 而不是不是。

So you probably want != instead of is not.

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