How Can I Efficiently Perform Element-Wise Addition of Lists in Python?

Element-Wise Addition of Lists: Pythonic Efficiency

When manipulating lists, the need to perform element-wise operations often arises. Consider the task of adding elements of two lists positionally, as shown below:

list1 = [1, 2, 3]
list2 = [4, 5, 6]

The desired output is:

[1, 2, 3]
+  +  +
[4, 5, 6]
|| || ||
[5, 7, 9]

To achieve this element-wise addition, several Pythonic approaches exist:

Method 1: operator.add and map

The operator.add module provides the necessary functionality for element-wise addition. By utilizing the map function, you can iterate through both lists simultaneously and apply the add operation:

from operator import add
result = list(map(add, list1, list2))

Method 2: zip and List Comprehension

The zip function combines elements of lists into tuples, which can be further manipulated in a list comprehension. This approach involves extracting values from the tuples and summing them:

result = [sum(x) for x in zip(list1, list2)]

Performance Considerations

The choice of method may depend on performance requirements. The following timing comparisons indicate that the map(add, list1, list2) approach is the fastest for large lists. The zip-based methods are slower due to the additional tuple manipulation.

For instance, with lists containing 100,000 elements each:

%timeit from operator import add;map(add, list1, list2)
10 loops, best of 3: 44.6 ms per loop
%timeit from itertools import izip; [a + b for a, b in izip(list1, list2)]
10 loops, best of 3: 71 ms per loop
%timeit [a + b for a, b in zip(list1, list2)]
10 loops, best of 3: 112 ms per loop

For more complex operations, additional methods may be required. However, for the simple task of element-wise addition, the approaches outlined above provide the most Pythonic and efficient solutions.

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