Get index in the list of objects by attribute in Python

问题

I have list of objects with attribute id and I want to find index of object with specific id. I wrote something like this:

index = -1
for i in range(len(my_list)):
    if my_list[i].id == 'specific_id'
        index = i
        break

but it doesn't look very well. Are there any better options?

回答1:

Assuming

a = [1,2,3,4]
val = 3

Do

a.index(val) if val in a else -1

For multiple occurrence, as per Azam's comment below:

[i if val == x else -1 for i,x in enumerate(a)] 

Edit1: For everyone commenting that its List of object, all you need is, access the id

[i if val == x.id else -1 for i,x in enumerate(a)] 

回答2:

Use enumerate when you want both the values and indices in a for loop:

for index, item in enumerate(my_list):
    if item.id == 'specific_id':
        break
else:
    index = -1

Or, as a generator expression:

index = next((i for i, item in enumerate(my_list) if item.id == 'specific_id'), -1)

回答3:

Here's an alternative that doesn't use an (explicit) loop, with two different approaches to generating the list of 'id' values from the original list.

try:
    # index = map(operator.attrgetter('id'), my_list).index('specific_id')
    index = [ x.id for x in my_list ].index('specific_id')
except ValueError:
    index = -1

回答4:

You can use enumerate:

for index, item in enumerate(my_list):
    if item.id == 'specific_id':
        break

来源：https://stackoverflow.com/questions/19162285/get-index-in-the-list-of-objects-by-attribute-in-python