Improve stubgen

[tharvik]

Add some type defaults to generated stubs.

For example

CONST = 1

class A:
    B = ''
    def __init__(self):
        self.c = None

get typed as

from typing import Any, Optional

CONST = ...  # type: int

class A:
    B = ...  # type: str
    c = ...  # type: Optional[Any]
    def __init__(self) -> None: ...

Do not support ~complex cases like

a, b = 1, 2

[JukkaL]

Looks good! One thing might need some tweaking. We probably shouldn't infer Optional[...] for x in the example below, since None is sometimes used as the default value for mutable instance variables, as x = [] would not be right in the class body. In this example we should probably infer Any as the type of x, at least if x is also assigned to in __init__:

class A:
    x = None
    def __init__(self):
        self.x = []

None initializers in __init__ can result in Optional[Any], since there is no reason not to initialize with [], for example. This is only relevant for class bodies.

[tharvik]

I've gone the easy way and simply infer Any for the None cases.

[JukkaL]

It would still be nice to infer Optional[Any] for functions arguments with a default None value. Would it be difficult to special case function arguments this way?

[tharvik]

Okay, added, not very pretty but a nicer way (not special case) would require some structural changes.

[tharvik]

Also added a test case about it.

[JukkaL]

Thanks!

[gvanrossum]

Thanks! I'm confused though -- it seems to generate type annotations only for arguments that have defaults?

[JukkaL]

Yeah, it would be nice to generate : Any annotations for arguments without defaults.

[gvanrossum]

But what if the code is already annotated? Shouldn't that annotation just be copied into the stub? We've been discussing use cases for such behavior.

[JukkaL]

That would be nice as well, but stubgen can't do that yet. I can create an issue for that. Also, for type checked code stubgen could run type checking to infer types, but it wouldn't be desirable for unannotated modules as this could result in type errors or even crashes.