How to Modify a List Within a Function in Python: Pass by Reference or In-Place Modification?

Modifying a List inside a Function

When working with list parameters in functions, the references passed to the function point to the original list. Any modifications made to the list_arg variable within the function are confined to its local scope and won't affect the original list.

To circumvent this issue and modify the original list, one needs to directly assign elements to the list instead of reassigning the entire list to a new value. Here's an example:

def function1(list_arg):
   a = function2()    # function2 returns an array of numbers
   list_arg[:] = list(a)

list1 = [0] * 5
function1(list1)
print(list1)  # [1, 2, 3, 4, 5]

In this modified code, we use the slice notation list_arg[:] to assign the elements of list(a) to the original list, effectively modifying the list in place.

It's important to note that while in-place modifications may seem convenient, they can become difficult to comprehend and may lead to confusion for developers maintaining the code. Explicit reassignments are generally preferred for clarity and readability.

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