Circular Reference with python lists

Question

Can someone explain this?

>>> x=x[0]=[0]
>>> x
[[...]]
>>> x is x[0]
True
>>> x[0][0][0][0][0][0][0]
[[...]]
>>>         


        

Answer 1

That's just Python telling you that you have a circular reference; it's smart enough not to enter an infinite loop trying to print it out.

Answer 2

iPython will do this:

[<Recursion on list with id=38505216>]

It's the same thing; the interpreter telling you that you have a recursive data structure.

Answer 3

It's output by the method responsible for generating the representation of the structure. It represents a recursive structure, elided since it can be nested infinitely.