class_init_decorator.py

# this is untested
from functools import wraps
from itertools import chain

def autoassign(init_method): # decorator
    """
    @autoassign
    def __init__(self, a: int, b: float):
        pass

    becomes:

    def __init__(self, a: int, b: float):
        self.a = a
        self.b = b
        pass
    """
    args, varargs, varkw, defaults, \
    kwonlyargs, kwonlydefaults, annotations \
        = inspect.getfullargspec(init_method)

    assert varargs is None
    assert varkw is None

    @wraps(init_method)
    def wrapper(self, *args, **kwargs):
        for name, value in zip(args[1:], chain(args, kwonlyargs)):
            setattr(self, name, value)
        for name, value in kwargs.items():
            setattr(self, name, value)
        return init_method(self, *args)

    return new_init_method