python - Why does list(my_list) modify the object?

Question

I happened on this peculiar behaviour accidentally:

>>> a = []
>>> a[:] = ['potato', a]
>>> print a
['potato', [...]]
>>> print list(a)
['potato', ['potato', [...]]]

By what mechanism does calling list(a) unroll one level of recursion in the string representation of itself?

Answer 1

The ... is only displayed when an item contains itself -- that is, the same object. list(a) makes a copy of the list, so the inner a isn't the same object. It only shows the ... when it gets to "a inside a", not "a inside list(a)".