I am curious why ValueErrors are different in List and Tuple when I try to get an index.  ValueError of a list returns in well format with actual argument "ValueError: 'ITEM' is not in list", whereas tuple returns something like this "ValueError: tuple.index(x): x not in tuple". 
I think List and Tuple both are calling same index() method then why it is raising different ValueErrors? 
>>> jframe_li
['Angular', 'React', 'Vue.js', 'Ember.js', 'Mereor', 'Node.js', 'Backbone.js']
>>> jframe_tu
('Angular', 'React', 'Vue.js', 'Ember.js', 'Mereor', 'Node.js', 'Backbone.js')
>>> jframe_li.index('React')
1
>>> jframe_tu.index('React')
1
>>> jframe_li.index('react')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ValueError: 'react' is not in list

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

This seems to be related to argument clinic work (issue 20186 and issue 20185).

Thus is definitely is not related to Argument Clinic.

And seems that this issue is a duplicate of an old issue with a long discussion and an unfinished patch, but currently I cannot find that issue.

> And seems that this issue is a duplicate of an old issue with a long discussion and an unfinished patch, but currently I cannot find that issue.

possibly duplicate of issue13349 which was rejected ?

Yes, it is. Thank you Karthikeyan!