How would a typing system know if the right type is `int` or `Optional[int]` or `Union[int, str]` or something else? The only right thing is to type the argument as `Any` in the absence of a type declaration.
The typing system should use the most specific valid type, and the code author can broaden it with explicit typing if needed. No good typing system should ever infer a variable as `Any`: "I don’t know the type of this" (`unknown` in TypeScript) is not the same thing as "This function accepts anything". Conflating these things is one of the main reasons why Mypy is so annoying.
A typing system should only infer things that it knows are true, it should never invent restrictions. In a language like Python that is duck-typed, `Any` is the only reasonable choice in the absence of other real constraints like a type-annotation.
def f(i=0) -> None:
if i is None:
do_something()
else:
do_something_else()
Yeah, I know it's retarded. I don't expect high quality code in a code base missing type annotation like that. Assuming `i` is `int` or `float` just makes incrementally adoption of a type checker harder.
No it’s not. The typing system should use the most specific type available, and it’s your responsability to broaden it if needed. That’s how it works in all statically-typed languages.
I want a typing system with a good inference that doesn’t require me to type each and every variable, just like in any good statically-typed language like OCaml or Typescript. Strong typing and explicit typing are two very different things.
It's guaranteed to be correct if you use different operators for ints and floats, which is what at least some ML dialects (notably, OCaml) do precisely so that types can be inferred from usage.
That's the downside of operator overloading - since it relies on types to resolve, they need to be known and can't be inferred.
I was merely giving an example that strong typing has nothing to do with having to write the types. (and, obviously, the inferred type (int -> int) is correct. )