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.