List of lists changes reflected across sublists unexpectedly

I created a list of lists:

>>> xs = [[1] * 4] * 3
>>> print(xs)
[[1, 1, 1, 1], [1, 1, 1, 1], [1, 1, 1, 1]]

Then, I changed one of the innermost values:

>>> xs[0][0] = 5
>>> print(xs)
[[5, 1, 1, 1], [5, 1, 1, 1], [5, 1, 1, 1]]

I expected this to only affect the first sublist, not all of them. That is:

>>> print(xs)
[[5, 1, 1, 1], [1, 1, 1, 1], [1, 1, 1, 1]]

Why did every first element of every sublist change to 5?

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See also:

• How do I clone a list so that it doesn't change unexpectedly after assignment? and

  How to initialize a two-dimensional array (list of lists, if not using NumPy) in Python? for workarounds for the problem

• List of dictionary stores only last appended value in every iteration for an analogous problem with a list of dicts

• How do I initialize a dictionary of empty lists in Python? for an analogous problem with a dict of lists