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But I found a real bug to use a tuple with a comma.
Python3 recognized "abc", expression as tuple of one element.
But type() and len() recognize "abc", expression as "abc" string.
So now, I found a real bug.
I'll show you below sentences.
>>> "abc",
('abc',)
>>> obj = "abc",
>>> obj
('abc',)
>>> type(obj)
<class 'tuple'>
>>> len(("abc",))
1
>>> len(obj)
1
>>> type("abc",)
<class 'str'>
>>> len("abc",)
3

What you're seeing is a feature of the grammar.
Function allow an optional trailing comma in the argument list:
 >>> pow(2, 5)
 32
 >>> pow(2, 5,)
 32
So, to create a tuple inside in an argument list, you need the extra layer of parentheses.
Sorry, this isn't a real bug. It is just a conflict resolution between use of a comma to separate arguments in a function call and use of a comma to create a tuple.