Python Program to Iterate Through Two Lists in Parallel

Python Program to Iterate Through Two Lists in Parallel

In this example, you will learn to iterate through two lists in parallel.

To understand this example, you should have the knowledge of the following Python programming topics:

Example 1: Using zip (Python 3+)

list_1 = [1, 2, 3, 4]
list_2 = ['a', 'b', 'c']

for i, j in zip(list_1, list_2):
    print(i, j)

Output

1 a
2 b
3 c

Using zip() method, you can iterate through two lists parallel as shown above.

The loop runs until the shorter list stops (unless other conditions are passed).

Example 2: Using itertools (Python 2+)

import itertools

list_1 = [1, 2, 3, 4]
list_2 = ['a', 'b', 'c']

# loop until the short loop stops
for i,j in zip(list_1,list_2):
    print(i,j)

print("\n")

# loop until the longer list stops
for i,j in itertools.zip_longest(list_1,list_2):
    print(i,j)

Output

1 a
2 b
3 c


1 a
2 b
3 c
4 None

Using the zip_longest() method of itertools module, you can iterate through two parallel lists at the same time. The method lets the loop run until the longest list stops.

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