List Linking Issue in List Initialization with [[]] * n

When initializing a list of lists using [[]] n, programmers often encounter an unexpected issue where the lists appear to be linked together. This occurs because the [x]n syntax creates multiple references to the same underlying list object, rather than creating distinct list instances.

To illustrate the problem, consider the following code:

x = [[]] * 3
x[1].append(0)
print(x)

The output of this code is:

[[0], [0], [0]]

Instead of the expected output:

[[], [0], []]

The issue stems from the fact that each element in the list is a reference to the same list object. When one of the elements is modified, all other elements are affected.

To create a list of truly distinct lists, the correct approach is to use list comprehension:

x = [[] for i in range(3)]

This syntax creates a new list object for each element in the list, ensuring that they are independent.

The following code serves as a demonstration:

In [20]: x = [[]] * 4

In [21]: [id(i) for i in x]
Out[21]: [164363948, 164363948, 164363948, 164363948] # same id()'s for each list,i.e same object


In [22]: x=[[] for i in range(4)]

In [23]: [id(i) for i in x]
Out[23]: [164382060, 164364140, 164363628, 164381292] #different id(), i.e unique objects this time