Question

a = [[1,2,3],[4,5,6]]

I would like to get 0 for 1,2 and 3 and to get 1 for 4, 5 and 6.

of course I can do something like that:

def get_index(my_list, my_item):
    for i, j in enumerate(my_list):
        if my_item in j:
            return i
    raise ValueError("Item not in any list")

Is there a better way of doing it?

Answer 1

Updated Answer:

This is an improved version of my original answer, thanks to input from zenply, the OP.

b = [[1,2,3],[4,5,6],[1,4,5], [4,7,8]]

def create_dict_2(a):
    my_dict = {}
    for index, sublist in enumerate(a):
        for ele in sublist:
            if not ele in my_dict:
                my_dict[ele] = index
    return my_dict

Result:

>>> my_dict = create_dict(b)
>>> my_dict[4]
1
>>> my_dict[5]
1
>>> my_dict[1]
0
>>> my_dict[7]
3