Python: Add two given lists of different lengths, start from left, use itertools module

Last update on July 12 2025 13:09:26 (UTC/GMT +8 hours)

37. Add Lists from Left

Write a Python program to add two given lists of different lengths, starting from the left, using the itertools module.

Sample Solution:

Python Code:

from itertools import zip_longest

def elementswise_left_join(l1, l2):
    result = [a + b for a,b in zip_longest(l1, l2, fillvalue=0)][::1]
    return result

nums1 = [2, 4, 7, 0, 5, 8]
nums2 = [3, 3, -1, 7]
print("\nOriginal lists:")
print(nums1)
print(nums2)
print("\nAdd said two lists from left:")
print(elementswise_left_join(nums1, nums2))

nums3 = [1, 2, 3, 4, 5, 6]
nums4 = [2, 4, -3]
print("\nOriginal lists:")
print(nums3)
print(nums4)
print("\nAdd said two lists from left:")
print(elementswise_left_join(nums3, nums4))

Sample Output:

Original lists:
[2, 4, 7, 0, 5, 8]
[3, 3, -1, 7]

Add said two lists from left:
[5, 7, 6, 7, 5, 8]

Original lists:
[1, 2, 3, 4, 5, 6]
[2, 4, -3]

Add said two lists from left:
[3, 6, 0, 4, 5, 6]

For more Practice: Solve these Related Problems:

• Write a Python program to add two lists of different lengths from the left side using itertools.zip_longest, padding with zero on the left.
• Write a Python program to sum corresponding elements from two lists starting from the left and then map a lambda to square each result.
• Write a Python program to use itertools.zip_longest to add two lists element-wise from the left and then filter out sums that are prime.
• Write a Python program to combine two lists of different lengths from the left side and then compute the cumulative sum of the results.

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Python Code Editor:

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