\' \' vs. \'extend()\': Which is the Pythonic Way to Concatenate Lists?

Concatenating Lists in Python: The Difference Between ' =' and extend()

When joining multiple lists in Python, the = and extend() methods offer two distinct approaches. This article will explore the nuances between these options and determine the "pythonic" way to perform list concatenation.

The ' =' Operator

The = operator, also known as the "in-place addition" operator, modifies the list in place by appending the elements of the second list.

<code class="python">a = [1, 2]
b = [2, 3]
b += a</code>

After this operation, the b list becomes [2, 3, 1, 2].

The extend() Method

The extend() method, on the other hand, extends the list by appending the elements of the second list without modifying the original list.

<code class="python">a = [1, 2]
b = [2, 3]
b.extend(a)</code>

In this case, the b list becomes [2, 3, 1, 2] as well.

Performance Considerations

On a bytecode level, the only difference between these methods is that extend() involves a function call, which has a slightly higher performance overhead than the in-place addition performed by =. However, this difference is negligible unless the concatenation operation is performed millions of times.

Which Method is Pythonic?

Ultimately, both = and extend() are Pythonic for list concatenation, with the choice depending on preference. = is more concise and doesn't create an extra list, while extend() maintains the immutability of the original list.

For typical use cases where performance is not a concern, either method is acceptable. However, in time-sensitive applications, = may provide a slight performance advantage.

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