如何检查python对象列表中是否存在值

您可以使用内置函数在一行中完成此操作 any

if any(obj['shape'] == 'square' for obj in shapes):
    print('There is a square')

不过,这相当于for-loop方法。

index = next((i for i, obj in enumerate(shapes) if obj['shape'] == 'square'), -1)

然而,这已经足够复杂了,所以最好只使用正常的for循环。

index = -1
for i, obj in enumerate(shapes):
    if obj['shape'] == 'square':
        index = i
        break

看,马,没有循环。

import json
import re

if re.search('"shape": "square"', json.dumps(shapes), re.M):
    ... # "square" does exist

如果要检索与 square ,您需要使用 for...else

for i, d in enumerate(shapes):
    if d['shape'] == 'square':
        break
else:
    i = -1

print(i) 

表演

100000 loops, best of 3: 10.5 µs per loop   # regex
1000000 loops, best of 3: 341 ns per loop   # loop

使用 list comprehension 您可以执行以下操作:

if [item for item in shapes if item['shape'] == 'square']:
    # do something

filter() :

if list(filter(lambda item: item['shape'] == 'square', shapes)):
    # do something

get 要获得更稳健的解决方案:

if any(i.get("shape", "none") == "square" for i in shapes):
    #do something
    pass

仅在存在时检查:

any(shape.get('shape') == 'square' for shape in shapes)

获取第一个索引(如果它不存在,您将获得StopIteration异常)。

next(i for i, shape in enumerate(shapes) if shape.get('shape') == 'square')

所有索引:

[i for i, shape in enumerate(shapes) if shape.get('shape') == 'square']

import operator
shape = operator.itemgetter('shape')
shapez = map(shape, shapes)
print('square' in shapez)