Better typing support

[LecrisUT]

We should make use of:

• warnings.deprecated with backport in typing_extensions. This would replace the deprecated package to include typing support
• Marking functions as abstract and Final
• __future__.annotations

[mfocko]

Currently a low-prio… Also a note, with regards to the @abstractmethod, I have tried to switch that, IIRC we also use the instances of abstract classes in the tests, so it's not that trivial to achieve (and we're already in a mock hell)

[LecrisUT]

I guess the issue is with

Using this decorator requires that the class’s metaclass is ABCMeta or is derived from it. A class that has a metaclass derived from ABCMeta cannot be instantiated unless all of its abstract methods and properties are overridden.

Hmm, if you don't add an ABC it seems to work fine as just a type-hint:

>>> import abc
... 
... class A:
...     @abc.abstractmethod
...     def hello(self):
...         raise NotImplementedError
... 
... class B(A):
...     def hello(self):
...         print("hello")
... 
... class C(A):
...     pass
... 
... a = A()
... b = B()
... c = C()
... b.hello()
... c.hello()
... 
hello
Traceback (most recent call last):
  File "<python-input-2>", line 19, in <module>
    c.hello()
    ~~~~~~~^^
  File "<python-input-2>", line 6, in hello
    raise NotImplementedError
NotImplementedError