functools_total_ordering_abc_mypy.py

# running mypy on this file fails:
#  error: Only concrete class can be given where "Type[Student]" is expected
import abc
import functools

# https://docs.python.org/3/library/functools.html#functools.total_ordering
@functools.total_ordering
class Student(abc.ABC):
    def __init__(self, firstname: str, lastname: str):
        self.firstname = firstname
        self.lastname = lastname

    def _is_valid_operand(self, other):
        return (hasattr(other, "lastname") and
                hasattr(other, "firstname"))

    def __eq__(self, other):
        if not self._is_valid_operand(other):
            return NotImplemented
        return ((self.lastname.lower(), self.firstname.lower()) ==
                (other.lastname.lower(), other.firstname.lower()))

    def __lt__(self, other):
        if not self._is_valid_operand(other):
            return NotImplemented
        return ((self.lastname.lower(), self.firstname.lower()) <
                (other.lastname.lower(), other.firstname.lower()))

    @abc.abstractmethod
    def get_record(self) -> str:
        pass

class NewStudent(Student):
    def get_record(self) -> str:
        return f"{self.lastname}, {self.firstname}"