Why Do Changes to One Sublist Affect All Sublists in a Python List of Lists Created Using `[x] * n`?

List of Lists: Unexpected Changes Across Sublists Explained

In Python, when creating a list of lists, using [x] * n will result in a list with multiple references to the same underlying list. This behavior can lead to unexpected changes in all sublists when modifying values in one sublist.

For example, consider the following code:

xs = [[1] * 4] * 3

This code creates a list of lists, where each sublist references the same underlying list of four 1s. When we change one of the elements in the sublist:

xs[0][0] = 5

The changes are reflected across all sublists. This occurs because the original list of lists only has three references to the same underlying sublist, not three distinct sublists.

To create separate sublists with distinct values, you can use a list comprehension:

xs = [[1] * 4 for _ in range(3)]

In this case, the list comprehension creates a new list of four 1s for each element in the new list of lists, resulting in three distinct sublists.

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