@gvanrossum, I gave the issue more thought and I'm probably going ahead with the Python implementation since callable genericalias seems contentious. In the future someone else can just replace the Python version with the C version if it comes to fruition.

Supporting __args__ for a Callable[[int, str], dict] as ((int, str), dict) is surprisingly rather inconvenient work. A few typing methods have to become recursive to account for nested tuples of types (mainly the ones that check for TypeVars and replacement of TypeVars). The C counterparts to those methods have to become recursive too. Update: We can represent the internal args as (Tuple[int, str], dict) which avoids the need for recursion.

Although __args__ of ((int, str), dict) is the cleanest IMO, the effort to achieve it versus just making both __args__ (int, str, dict) feels disproportionately high. Maybe this is why the original code author for typing (I'd assume Ivan) made a conscious decision to flatten the args.

Edit: Sorry about the force push, I'm not a git sensei :(.