> There is nothing special about map and filter, they are not idiomatic Python because there are better ways to do the same things. True, list comprehension is

> There is nothing special about map and filter, they are not idiomatic Python because there are better ways to do the same things. True, list comprehension is often used instead. But a complete typing system should be able to type-check that too. The point is not changed. Also, I only used map and filter as an example. Python programmers tend to write a lot of generics functions without actually knowing it. def f(g, *args): ... r = g(*args) ... return r This function is actually quite generic, akin to map. And we are not yet getting into the realm of "trait" or "concept" or "typeclass" or whatever. def sum(*nums): s = 0 for n in nums: s += n return s Remember, although s is definitely an int, s + n may yield some completely unrelated type if n implements __radd__. The function here involves potentially infinite number of types, and their __add__ or __radd__ traits (reusing the name of the Python magic method). To fully express its type without unnecessary constraints is an interesting exercise. Since Python allows dynamic parameter list building (like sum(*nums)), dependent typing may be necessary for that purpose.