There are two empty typing.Tuple. They have the same repr but are not equal.

>>> from typing import *
>>> t1 = Tuple[()]
>>> t2 = t1.copy_with(())
>>> t1
typing.Tuple[()]
>>> t2
typing.Tuple[()]
>>> t1 == t2
False
>>> t1.__args__
((),)
>>> t2.__args__
()

The only differences is that one has empty __args__, while other has __args__ containing an empty tuple. There is a code purposed to make __args__ containing an empty tuple in this case. What is the purpose?

It is not pure theoretical question. This affects unpacked TypeVarTuple substitution. With natural implementation Tuple[Unpack[Ts]][()] is not equal to Tuple[()] and I still have not figured which and where code should be added to handle this special case. It would be easier if such special case did not exist.

Built-in tuple does not have a special case:

>>> tuple[()].__args__
()

Alas, I have no idea. I don't even recall what copy_with() is for (it was apparently introduced in 3.7). Possibly vopy_with() is wrong here? I imaging some of this has to do with the special casing needed so that repr() of an empty Tuple type doesn't print "Tuple[]" (which IIRC it did, long ago).

If for repr(Tuple[()]), it is no longer needed.

New changeset 15df8f8d89a0e563bdd15e4cd6734298736a5a1d by Serhiy Storchaka in branch 'main':
bpo-46981: Remove typing._TypingEmpty (GH-31836)
https://github.com/python/cpython/commit/15df8f8d89a0e563bdd15e4cd6734298736a5a1d

I tried out 3.11 on my pyanalyze type checker and got some failures because of this change, because my previous trick for distinguishing between Tuple and Tuple[()] failed.

3.10:

>>> from typing import get_args, Tuple
>>> get_args(Tuple[()])
((),)
>>> get_args(Tuple)
()


3.11:

>>> from typing import get_args, Tuple
>>> get_args(Tuple[()])
()
>>> get_args(Tuple)
()

However, the new behavior is more consistent: get_args(tuple[()]) always returned (). It's also easy enough to work around (just check `... is Tuple`).

I'll put a note in the What's New for 3.11 about this change.