The tuple.index() method returns an error message that does not allow users to know what element was being looked for inside the tuple:

>>> ().index(1)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ValueError: tuple.index(x): x not in tuple

The list.index() method has a much better error message:

>>> [].index(1)   
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ValueError: 1 is not in list

We could improve tuple.index() so that its behaviour becomes similar to that of list.index().

This is a duplicate of issue13349.