Since Python 3.3 a bug was fixed meaning the property() decorator is now correctly identified as abstract when applied to an abstract method.

Note: Order matters, you have to use @property above @abstractmethod

Python 3.3+: (python docs):

from abc import ABC, abstractmethod

class C(ABC):
    @property
    @abstractmethod
    def my_abstract_property(self):
        ...

Python 2: (python docs)

from abc import ABCMeta, abstractproperty

class C:
    __metaclass__ = ABCMeta

    @abstractproperty
    def my_abstract_property(self):
        ...

Starting with Python 3.3, it is possible to combine @staticmethod and @abstractmethod, so none of the other suggestions are necessary anymore:

@staticmethod
@abstractmethod
def my_abstract_staticmethod(...):

@abstractstaticmethod has been deprecated since version 3.3 (but is still there in Python 3.14).

It looks like mypy doesn't understand the abstractclassmethod decorator. That decorator has been deprecated since Python 3.3, as the abstractmethod and classmethod decorators were updated to play nice together. I think your code will work properly if you do:

@classmethod
@abstractmethod 
def from_data(cls: Type[ElementT], data: int) -> ElementT:
    pass

It's unrelated to your type checking issues, but you probably also want to change ElementBase to inherit from abc.ABC or to explicitly request the abc.ABCMeta metaclass if you want the abstractness of the class to be enforced by Python. Regular classes don't care about the abstractmethod decorator, and so as written, you'll be able to instantiate ElementBase (or you could if it's __init__ method didn't have an unrelated issue).

And another peripherally related note on this kind of type hinting... PEP 673 will add typing.Self in Python 3.11, which will be a convenient way for a method to refer to the type of object it's being called on. It should play nicely with classmethods without requiring you to jump through any hoops. With it you'd be able to write this much simpler version of the annotations:

@classmethod
@abstractmethod
def from_data(cls, data: int) -> Self:
    pass

Before abc was introduced you would see this frequently.

class Base(object):
    def go(self):
        raise NotImplementedError("Please Implement this method")


class Specialized(Base):
    def go(self):
        print "Consider me implemented"