Home > Article > Backend Development > \" \" vs. \"extend()\": Which is the Pythonic Way to Concatenate Lists?
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, 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, 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.
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.
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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