Python List Addition: When to Use ` =` (iadd) vs ` ` (add)?

Augmented Assignment vs. Assignment

The Python programming language offers two distinct operators for list addition: iadd and __add__. While they both perform similar functions, there exists a crucial difference in their behaviors.

iadd (Augmented Assignment)

Consider the following code snippet:

x = y = [1, 2, 3, 4]
x += [4]

When using __iadd__, the original list (x) is directly modified, resulting in both x and y pointing to the same updated list.

add (Assignment)

Conversely, using add creates a new list as seen below:

x = y = [1, 2, 3, 4]
x = x + [4]

In this case, add generates a fresh list that contains the combined elements of x and [4]. However, since the assignment is to x, only x points to the new list, leaving y unchanged.

Explanation

iadd is designed for in-place modification of a list. It mutates the existing list without creating a new one. This behavior is particularly useful when optimizing memory usage or when maintaining references to the updated list.

On the other hand, add creates a completely distinct list. This is suited for scenarios where the original list needs to remain unchanged or when a copy of the modified list is desired.

In summary, iadd modifies the original list while add generates a new list. Understanding this distinction is crucial for effective list manipulation in Python.

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