Python - is list's index() method 1-based instead of 0-based?

Question

Consider the following output:

a = list()
a.append(7)
a.extend([4,2])
a += [5]
a.insert(0,3)
print(a)
print(a.index(4))

Answer 1

The resulting list is

[3,7,4,2,5]

a.index(4) returns 2.

Quoting the docs, https://docs.python.org/3.7/tutorial/datastructures.html

list.index(x) "returns zero-based index in the list of the first item whose value is equal to x. "

This agrees with the observed output. What a.index(4) does, is that it searches the list for the first element of value 4 occuring in the list, and returns the index of that element.

Answer 2

I was confused by "2" in list 😅