iterate through a list and restart index_1 at 0 if list index is out of range-CodePudding

I am trying to make a program where I have a list my_list_1 = [1,2,3,...] and a second list `my_list_2 = [1,2,3,...] and len(my_list_1) < len(my_list_2). I want to iterate through the lists like this:

my_list_1 = [1,2,3]
my_list_2 = [5,6,7,8,9]
result = []

for i in range(len(my_list_2)):
    result.append(my_list_1[i]   my_list_2[i])
    # i == 0: 1   5 = 6
    # i == 1: 2   6 = 8
    # i == 2: 3   7 = 10
    # i == 3: 1   8 = 9
    # i == 4: 2   9 = 11
    """ what I want to happen is when i > len(my_list_1), instead of giving a index out of range
        error, I want the loop to start at the beginning if the smaller list"""

I tried something like this:


for i in range(len(my_list_2)):
    if i % (len(my_list_1) - 1) == 0 or i == 0:
        x = 0
    else:
        x =1
   result.append(my_list_1[x]   my_list_2[i])

for i in range(len(my_list_2)):
   if x == (len(my_list_1) - 1) or i == 0:
       x = 0
   else:
       x  = 1
   result.append(my_list_1[x]   my_list_2[i])

this works but I am looking for something a bit more elegant and possibibly even making a copy of my_list_1 and extend it to the length of my_list_2 so that it would look like this:

>>> my_list_1 = [1,2,3]
>>> my_list_2 = [5,6,7,8,9]
>>> extend_list(my_list_1, len(my_list_2))
[1,2,3,1,2]

CodePudding user response：

You can also use itertools.cycle to create a cyclical list iterator, and use zip for the iterator and the other list.

from itertools import cycle

my_list_1 = [1,2,3]
my_list_2 = [5,6,7,8,9]

# I use list comprehension here
result = [ a   b for a, b in zip(cycle(my_list_1), my_list_2) ]

print(result)
# [6, 8, 10, 9, 11]

CodePudding user response：

You just need modulo for the first index:

for i in range(len(my_list_2)):
    x = i % len(my_list_1)
    result.append(my_list_1[x]   my_list_2[i])