Concatenating Lists: ' ' vs. 'extend()'

When working with lists in Python, you may encounter two common ways to concatenate (combine) them: the extend() method and the plus ( ) operator. This article explores their differences and provides insights into the "pythonic" way of performing list concatenation.

'extend()' Method

The extend() method allows you to append the elements of another list to the original list. It doesn't modify the original list but returns None.

a = [1, 2]
b = [2, 3]
b.extend(a)

After this operation, b will contain the elements of both a and b: [2, 3, 1, 2].

' =' Operator

The = operator performs in-place addition on the list. It directly modifies the original list and appends the elements of the other list to it.

b  = a

Here, b will also contain the combined elements: [2, 3, 1, 2].

Which is Pythonic?

Both methods are considered "pythonic" and have their own uses. However, the plus ( ) operator is generally preferred as it provides a more concise and consistent syntax for list concatenation. It is also marginally faster on a bytecode level as it avoids a function call involved with extend().

Difference in Execution

The only notable difference between the two methods is in their execution. extend() involves a function call, which is slightly more expensive in Python than the in-place addition performed by the = operator.

Conclusion

When concatenating lists in Python, the ' ' operator is the preferred "pythonic" approach. While extend() may be useful in certain circumstances, the = operator offers concise syntax, in-place modification, and slightly faster execution. However, performance optimizations should not be a significant concern unless list concatenation is performed excessively.