如何从字典中删除项目，同时迭代？

问题描述

在迭代过程中从Python中删除项目是否合法？

Is it legitimate to delete items from a dictionary in Python while iterating over it?

例如：

for k, v in mydict.iteritems():
   if k == val:
     del mydict[k]

想法是从字典中删除不符合特定条件的元素，而不是创建一个属于该字典的子字典的新字典被重复过来。

The idea is to remove elements that don't meet a certain condition from the dictionary, instead of creating a new dictionary that's a subset of the one being iterated over.

这是一个很好的解决方案吗？是否有更优雅/更有效的方式？

Is this a good solution? Are there more elegant/efficient ways?

推荐答案

控制台中的一个简单测试显示，您可以在迭代过程中修改字典：

A simple test in the console shows you cannot modify a dictionary while iterating over it:

>>> mydict = {'one': 1, 'two': 2, 'three': 3, 'four': 4}
>>> for k, v in mydict.iteritems():
...    if k == 'two':
...        del mydict[k]
...
------------------------------------------------------------
Traceback (most recent call last):
  File "<ipython console>", line 1, in <module>
RuntimeError: dictionary changed size during iteration

如delnan的回答中所述，删除条目会导致问题当迭代器尝试移动到下一个条目。相反，请使用 keys（）方法获取密钥列表，并与之配合使用：

As stated in delnan's answer, deleting entries causes problems when the iterator tries to move onto the next entry. Instead, use the keys() method to get a list of the keys and work with that:

>>> for k in mydict.keys():
...    if k == 'two':
...        del mydict[k]
...
>>> mydict
{'four': 4, 'three': 3, 'one': 1}

如果您需要根据项目值进行删除，请改用 items（）方法：

If you need to delete based on the items value, use the items() method instead:

>>> for k, v in mydict.items():
...     if v == 3:
...         del mydict[k]
...
>>> mydict
{'four': 4, 'one': 1}

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