python garbage collection about list append itself [duplicate]

Question

a = [2]
a.append(a)

And I print a,

[2, [...]]

Also I print a[1][0]

2

What is [...] ? and when I print a[1][0], print 2, not [...] ?

Answer 1

... is the ellipsis object. Here it is issued because else it would print forever! (due to infinite recursion)

and: print(a[1][0]):

a[1] is a so a[1][0] is 2, like a[1][1][1][1][0] is 2 too.

Answer 2

Ellipsis ... is used for slicing multidimensional numpy arrays.

The ellipsis syntax may be used to indicate selecting in full any remaining unspecified dimensions.

a[1] is [2, [...]]

so, a[1][0] is 2.