What happens when you append a list to itself? [duplicate]

Answer 1

Python lists contain references (similar to pointers) to objects. A list can refer to itself. Just don't try and recursively iterate through the list or you will end up with a stack overflow.

Answer 2

I think the output you are seeing becomes more clear if you add another element to the list. You have:

>>> x = []
>>> x.append(x)
>>> x
[[...]]

If we append another value to x:

>>> x.append(1)

Then we have:

>>> x
[[...], 1]

Here, [...] is just Python's way of representing the fact that the list is embedded in itself.

And of course:

>>> x[0]
[[...], 1]
>>> x[0][0][0]
[[...], 1]
>>>