ctypes stubs incomplete

[gvanrossum]

Sadly #454 leaves our code using ctypes a bunch of errors, not all of which are our fault. A few examples:

• wintypes.pyi is empty?!
• offset in from_buffer_copy() is optional
• apparently c_char*16 is valid to declare a 16-byte buffer

[euresti]

Couple of others:

• offset in from_buffer is optional
• As typed from_buffer and from_buffer_copy expect _CData as first argument
• from_buffer and from_buffer_copy return _CData instead of the class that is being created.
  (e.g.

 from ctypes import Structure, c_ulong, c_ushort

class POINT(Structure):
   _fields_ = [(u"x", c_ulong),
               (u"y", c_ulong),
               ]

p = POINT()

buf = bytearray(b'\00' * 8 + b'\01' + b'\00' * 7)
p2 = POINT.from_buffer_copy(buf)

reveal_type(p)    # Point
reveal_type(p2)  # _CData

• The attributes of Structure can't be accessed. So in the above p.x yields a type error.

[gvanrossum]

Fixing the return type of from_buffer()/from_buffer_copy() would require fixing python/mypy#1212; I think I'll use Any for now. This isn't great, but that bug is pretty subtle. Most other things are doable.

[gvanrossum]

Fixing c_char*16 is also problematic, because c_char is a class! The __mul__ operation is overloaded on the metaclass. But mypy doesn't support that yet. I think that's another case of python/mypy#1267.

[gvanrossum]

@matthiaskramm @tharvik How bad would it be if I just reverted #454? There's no way I can get our internal usages of ctypes to pass without fixing some tricky mypy issues (see previous comments). Putting # type: ignore in the stub won't be possible for these -- we'd have to ignore each call site of those features.

[tharvik]

wintypes.pyi is empty?!

It is not documented and only available on Windows (which I don't have).

Fixing c_char*16 is also problematic, because c_char is a class!

I found a way by using (not pretty, but working)

class _MulType(Generic[_T]):
    def __call__(self, *args: Any, **kwargs: Any) -> _T: ...
    def __mul__(self, size: int) -> _MulType[_T]: ...

c_int = ...  # type: _MulType[_SimpleCData[int]]

@gvanrossum I guess we can revert it but keep this issue open to have a remainder to do something when mypy is fixed.

[gvanrossum]

I've deleted the ctypes stub for now. After mypy 0.4.4 has been released (tomorrow?) I'll try to restore the previous version and improve it to the point where our internal code can pass with it.

[JukkaL]

There's also the option of annotation c_char with type Any. Again, not optimal, but some type checking is better than nothing.

[gvanrossum]

I think @tharvik's solution can be made to work, I just don't want to do it so close to the 0.4.4 release.

[JelleZijlstra]

We have pretty good ctypes stubs now.