How to Add Two Lists Elementwise in Python

Add two equal-length lists element by element using a list comprehension with zip, returning a new list of summed values.

Easy Python 3.9+ Aug 9, 2026 Algorithms & data structures 13 views 0 copies

list zip list-comprehension addition elementwise

Python code

8 lines

Python 3.9+

def elementwise_add(list1, list2):
    return [a + b for a, b in zip(list1, list2)]

if __name__ == "__main__":
    list_a = [1, 2, 3, 4]
    list_b = [10, 20, 30, 40]
    result = elementwise_add(list_a, list_b)
    print(result)

Output

stdout

[11, 22, 33, 44]

How it works

The zip function pairs the i-th element of list1 with the i-th element of list2, creating tuples like (1, 10), (2, 20), etc. The list comprehension [a + b for a, b in ...] unpacks each tuple into a and b and computes their sum, producing a new list. This approach is concise and avoids manual index tracking. It assumes both lists have equal lengths; if not, zip stops at the shorter list. For unequal lists, consider using itertools.zip_longest with a fill value.

Common mistakes

Forgetting that zip stops at the shorter list, silently ignoring extra elements
Modifying the original lists instead of creating a new result list
Manually iterating with indices when zip is simpler
Attempting to use + on lists directly, which concatenates instead of adding

Variations

Use `map` with an operator.add function: list(map(operator.add, list1, list2))
Use a for loop with an appended result list for readability

Real-world use cases

Combining sales totals from separate daily reports for each product into weekly figures.
Merging sensor readings from two devices at synchronized timestamps into a single stream.
Adding coordinate vectors in geometry or physics calculations before further analysis.

How to Add Two Lists Elementwise in Python

Python code

Output

How it works

Common mistakes

Variations

Real-world use cases

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Python code

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Variations

Real-world use cases

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