如何从字典列表中删除k，v项

Question

我想从现有json文件中删除不需要的值：

{ "items": [ { "id": "abcd", "h": 2, "x": 0, "level": 4 }, { "id": "dfgg", "h": 7, "x": 5, "level": 30 } ] }

我试着删除现有的值，但得到“dictionary changed size during iteration”。你知道吗

with open('inventory2.json', 'r') as inf:
    data = json.load(inf)
    inf.close()

    keysiwant = ['x', 'h']
    for dic in data['items']:
        for k, v in dic.items():
            if k not in keysiwant:
                dic.pop(k, None)

Answer 1

请试试这个。它使用较少的迭代，因为它首先过滤掉键，然后再将它们发送到pop/remove。而且，它只使用键（list（dic））而不是元组键/值。你知道吗

import json

t = """{ "items": [ { "id": "abcd", "h": 2, "x": 0, "level": 4 },
                    { "id": "dfgg", "h": 7, "x": 5, "level": 30 } ] }"""

data = json.loads(t)
keysiwant = ["x", "h"]

for dic in data["items"]:
    for k in (k for k in list(dic) if k not in keysiwant):
        dic.pop(k, None)

print(data)

输出：

{'items': [{'h': 2, 'x': 0}, {'h': 7, 'x': 5}]}

Answer 2

问题：dict.items()在python3中只是一个视图-不是dict项的副本-您不能在迭代时更改它。你知道吗

但是，您可以将dict.items()迭代器放入list()（这样可以复制它并将它与dict解耦）-然后可以迭代dict.items()的副本：

import json

t = """{ "items": [ { "id": "abcd", "h": 2, "x": 0, "level": 4 }, 
                    { "id": "dfgg", "h": 7, "x": 5, "level": 30 } ] }"""

data = json.loads(t)   # loads is better for SO-examples .. it makes it a mcve
keysiwant = ['x', 'h']
for dic in data['items']:
    for k, v in list(dic.items()):
        if k not in keysiwant:
            dic.pop(k, None)

print(data) 

输出：

{'items': [{'h': 2, 'x': 0}, {'h': 7, 'x': 5}]}

关于python2/python3的更多信息：in this answer到What is the difference between dict.items() and dict.iteritems()?