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?
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)
ValueError in the else clause (to mirror the behavior of list.index).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
list.find by analogy to the pair of str.find and str.index methods, but also mixed up which one raises a ValueError (it's str.index, not str.find) and which returns -1. Corrected to list.index now.You can use enumerate:
for index, item in enumerate(my_list):
if item.id == 'specific_id':
break
Implement the __eq__ method for your class
class MyCls:
def __init__(self, id):
self.id = id
def __eq__(self, other):
# comparing with str since you want to compare
# your object with str
if not isinstance(other, str):
raise TypeError("MyCls can be compared only with str")
if other == self.id:
return True
return False
now you can do something like
my_list = [MyCls(i) for i in 'abcdef']
print(my_list.index('c'))
This would return the index 2. It would behave like normal list.index methods behaves. i.e If it doesn't find the index, it will raise a ValueError
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)]
