User generic with TypeVarTuple does not check for minimal type of arguments

[serhiy-storchaka]

The following code:

from typing import *
T = TypeVar('T')
T2 = TypeVar('T2')
Ts = TypeVarTuple('Ts')
class A(Generic[T, T2, *Ts]):
    x: List[T]
    y: List[T2]
    z: Tuple[*Ts]

A[int]

is executed without errors. It is expected to get an error because A requires at least two arguments.

Without TypeVarTuple you get helpful errors.

class B(Generic[T, T2]):
    pass

B[int]
B[int, str, bytes]

TypeError: Too few arguments for <class '__main__.B'>; actual 1, expected 2

TypeError: Too many arguments for <class '__main__.B'>; actual 3, expected 2

[sobolevn]

The code says this:

cpython/Lib/typing.py

Lines 1833 to 1836 in f531b68

	# We only run this if there are no TypeVarTuples, because we
	# don't check variadic generic arity at runtime (to reduce
	# complexity of typing.py).
	_check_generic(cls, params, len(cls.__parameters__))

[AlexWaygood]

I believe that this has been fixed and backported (in #99412 and #99866). Closing as completed.

(Feel free to reopen if I'm incorrect.)