mypy: base class has no attribute x, how to type hint in base class

If you are using python 3.6 or later then

class Connector():
    short_name: str
    ...

should work. This doesn't actually exist in the namespace, but MYPY will find it. See https://www.python.org/dev/peps/pep-0526/.

---

Another option is to do

import abc
class Connector(abc.ABC):
    @property
    @abc.abstractmethod
    def short_name(self) -> str:
        ...

You'd add that attribute to the base type; you don't need to give it a value:

class Connector:
    short_name: str

This uses Python 3.6's Variable Annotation syntax, which is new in Python 3.6 or newer. It defines the type of an instance attribute, not a class attribute (for which there is a separate syntax).

You can use a comment otherwise, at which point you do have to give the attribute an initial value, and is a class attribute:

class Connector:
   short_name = ''  # type: str