In Python 3 and 2 docs https://docs.python.org/3.5/tutorial/datastructures.html, list.index only mentions the first argument:


list.index(x)

    Return the index in the list of the first item whose value is x. It is an error if there is no such item.

However, in reality list.index can take further arguments:

index(...)
    L.index(value, [start, [stop]]) -> integer -- return first index of value.
    Raises ValueError if the value is not present.