In Python, how can I find the index of the first item in a list that is NOT some value?

Question

Python\'s list type has an index(x) method. It takes a single parameter x, and returns the (integer) index of the first item in the list that has the value x.

Basica

Answer 1

[i for i, x in enumerate(my_list) if x != value][0]

If you're not sure whether there's a non-matching item, use this instead:

match = [i for i, x in enumerate(my_list) if x != value]
if match:
    i = match[0]
    # i is your number.

You can make this even more "functional" with itertools, but you will soon reach the point where a simple for loop is better. Even the above solutions aren't as efficient as a for loop, since they construct a list of all non-matching indices before you pull the one of interest.