Right now there's an uncovered branch inTypeVarTuple.__typing_prepare_subst__:

And it looks like there's a bug in it,these two lines:

forparaminenumerate(params[typevartuple_index+1:]):ifisinstance(param,TypeVarTuple):

Thisif's body will never be executed, becauseenumerate always returnstuple[int, T], it is neverTypeVarTuple.

So, I think that we need to removeenumerate() call here and add a test like:

>>>fromtypingimportGeneric,TypeVarTuple>>>V=TypeVarTuple('V')>>>T=TypeVarTuple('T')>>>classMy(Generic[*T]):pass...>>>My[*T,*V][*V]TypeError:MorethanoneTypeVarTupleparameterin__main__.My[*T,*V]

I will send a PR 😉