[英]How to check if value exists in python list of objects
if i have a simple list objects: 如果我有一个简单的列表对象:
shapes = [
{
'shape': 'square',
'width': 40,
'height': 40
},
{
'shape': 'rectangle',
'width': 30,
'height': 40
}
]
How can i quickly check if a shape
with value square
exists? 如何快速检查是否存在具有
square
值的shape
? I know I can use a for
loop to check each object, but is there a faster way? 我知道我可以使用
for
循环来检查每个对象,但是有没有更快的方法?
Thanks in advance! 提前致谢!
You can do this in one line with the builtin function any
: 您可以使用内置函数
any
一行完成此操作:
if any(obj['shape'] == 'square' for obj in shapes):
print('There is a square')
This is equivalent to the for-loop approach, though. 但是,这等效于for循环方法。
If you need to get the index instead, then there is still a one-liner that can do this without sacrificing efficiency: 如果您需要获取索引,那么仍然可以使用一种方法而不牺牲效率:
index = next((i for i, obj in enumerate(shapes) if obj['shape'] == 'square'), -1)
However, this is complicated enough that it's probably better to just stick with a normal for loop. 但是,这非常复杂,以至于坚持使用普通的for循环可能更好。
index = -1
for i, obj in enumerate(shapes):
if obj['shape'] == 'square':
index = i
break
Look ma, no loop. 看,没有循环
import json
import re
if re.search('"shape": "square"', json.dumps(shapes), re.M):
... # "square" does exist
If you want to retrieve the index associated with square
, you'd need to iterate over it using for...else
: 如果要检索与
square
相关的索引,则需要使用for...else
对其进行迭代:
for i, d in enumerate(shapes):
if d['shape'] == 'square':
break
else:
i = -1
print(i)
Performance 性能
100000 loops, best of 3: 10.5 µs per loop # regex
1000000 loops, best of 3: 341 ns per loop # loop
You can try this, using get
for a more robust solution: 您可以尝试使用
get
更强大的解决方案:
if any(i.get("shape", "none") == "square" for i in shapes):
#do something
pass
Using list comprehension you can do: 使用列表理解,您可以执行以下操作:
if [item for item in shapes if item['shape'] == 'square']:
# do something
if list(filter(lambda item: item['shape'] == 'square', shapes)):
# do something
Checking only if it exists: 仅检查是否存在:
any(shape.get('shape') == 'square' for shape in shapes)
Getting first index (you will get StopIteration exception if it does not exist). 获取第一个索引(如果不存在StopIteration异常,则该异常)。
next(i for i, shape in enumerate(shapes) if shape.get('shape') == 'square')
All indexes: 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)
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