Make get_type_hints not throw an error on builtin methods

[wheerd]

While builtin functions are supported, calling get_type_hints on a builtin method like object.__init__ causes an error. I change this to return an empty dictionary instead.

[ilevkivskyi]

Thank you for the PR!
I see that you also have opened an issue on b.p.o. http://bugs.python.org/issue29377 to add the types you need here to types module. I would prefer that these types are first added to types, and then you update this PR to use try: from types import ... except ImportError: WrapperDescriptorType = ...

[ilevkivskyi]

@wheerd After you take a look at my latest review on b.p.o., could you please update this PR using the try: from types import ... idiom I mentioned above and fix the lint issue?

[methane]

I don't like this isinstance chain.
How about this?

# global
_annotatable_types = (
    types.FunctionType,
    types.BuiltinFunctionType,
    types.MethodType,
    types.ModuleType,
    _wrapper_descriptor_type,
    _method_wrapper_type)

...

        if isinstance(obj, _annotatable_types):

[ilevkivskyi]

Thank, you! I have already noticed this some time ago, I would prefer to fix this separately after this PR is merged.

[ilevkivskyi]

@wheerd Could you please update the PR using the try: from types import ... idiom I mentioned in my first comment and fix the lint issue? Otherwise we could not move forward with this PR (I can't do this myself, since I can't merge a failing PR).

[wheerd]

Sorry I completely forgot about the pull request. Should be fixed now.

[ilevkivskyi]

Thanks!