Python Lists: Pass by Value or Reference?

List Manipulation in Python: Passing by Value vs. Reference

While working with lists in Python, one common challenge is the concept of passing by reference and understanding how it affects list changes. Let's explore a scenario to illustrate this issue:

a = ['help', 'copyright', 'credits', 'license']
b = a
b.append('XYZ')
print(b)  # ['help', 'copyright', 'credits', 'license', 'XYZ']
print(a)  # ['help', 'copyright', 'credits', 'license', 'XYZ']

In this example, you intend to append a value to list 'b,' but surprisingly, the value of list 'a' also changes. This is because, in Python, lists (and other objects) are passed by reference, which means they share the same memory location.

So, when you assign 'b' to 'a,' you're not creating a new list but referencing the same one. Therefore, any changes made to one list will be reflected in the other.

How to Pass by Value

To avoid unintended changes, you need to create a new list that's a copy of the original. In Python, slicing can be used to achieve this:

b = a[:]

By using the slice operator [:] on list 'a,' you create a new list 'b' that contains all elements of 'a' but occupies a separate memory location. Now, any changes made to 'b' will not affect 'a.'

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