if i have a simple list objects:
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? I know I can use a for loop to check each object, but is there a faster way?
Thanks in advance!
You can do this in one line with the builtin function any:
if any(obj['shape'] == 'square' for obj in shapes):
print('There is a square')
This is equivalent to the for-loop approach, though.
If you need to get the index instead, then there is still a one-liner that can do this without sacrificing efficiency:
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.
index = -1
for i, obj in enumerate(shapes):
if obj['shape'] == 'square':
index = i
break
Look ma, no loop.
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:
for i, d in enumerate(shapes):
if d['shape'] == 'square':
break
else:
i = -1
print(i)
Performance
100000 loops, best of 3: 10.5 µs per loop # regex
1000000 loops, best of 3: 341 ns per loop # loop
'square' in map(operator.itemgetter('shape'), shapes)
Using list comprehension you can do:
if [item for item in shapes if item['shape'] == 'square']:
# do something
Using filter():
if list(filter(lambda item: item['shape'] == 'square', shapes)):
# do something
You can try this, using get for a more robust solution:
if any(i.get("shape", "none") == "square" for i in shapes):
#do something
pass
Checking only if it exists:
any(shape.get('shape') == 'square' for shape in shapes)
Getting first index (you will get StopIteration exception if it does not exist).
next(i for i, shape in enumerate(shapes) if shape.get('shape') == 'square')
All indexes:
[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)
any(shape.get('shape') == 'square' for shape in shapes)