Using type (or any other subclass of type, e.g. a custom metaclass) as the type hint for one of the parameters of a function of a multimethod makes the dispatch process raise a TypeError when calling type.mro() (which expects the type object as an argument).
Example
@multimethod
def f(x: type):
print("success")
Expected
>>> f(int)
success
Actual
>>> f(int)
TypeError: unbound method type.mro() needs an argument
Traceback:
```
Traceback (most recent call last):
File "C:\Users\Paolo\Code\JB-PycharmProjects\LoveLetter\venv\lib\site-packages\IPython\core\interactiveshell.py", line 3418, in run_code
exec(code_obj, self.user_global_ns, self.user_ns)
File "", line 1, in
f(int)
File "C:\Users\Paolo\Code\JB-PycharmProjects\LoveLetter\venv\lib\site-packages\multimethod\__init__.py", line 184, in __call__
return self[tuple(map(self.get_type, args))](*args, **kwargs)
File "C:\Users\Paolo\Code\JB-PycharmProjects\LoveLetter\venv\lib\site-packages\multimethod\__init__.py", line 184, in __call__
return self[tuple(map(self.get_type, args))](*args, **kwargs)
File "C:\Users\Paolo\Code\JB-PycharmProjects\LoveLetter\venv\lib\site-packages\multimethod\__init__.py", line 174, in __missing__
groups = groupby(signature(types).__sub__, self.parents(types))
File "C:\Users\Paolo\Code\JB-PycharmProjects\LoveLetter\venv\lib\site-packages\multimethod\__init__.py", line 17, in groupby
groups[func(value)].append(value)
File "C:\Users\Paolo\Code\JB-PycharmProjects\LoveLetter\venv\lib\site-packages\multimethod\__init__.py", line 104, in __sub__
return tuple(mro.index(cls if cls in mro else object) for mro, cls in zip(mros, other))
File "C:\Users\Paolo\Code\JB-PycharmProjects\LoveLetter\venv\lib\site-packages\multimethod\__init__.py", line 104, in
return tuple(mro.index(cls if cls in mro else object) for mro, cls in zip(mros, other))
File "C:\Users\Paolo\Code\JB-PycharmProjects\LoveLetter\venv\lib\site-packages\multimethod\__init__.py", line 103, in
mros = (subclass.mro() for subclass in self)
TypeError: unbound method type.mro() needs an argument
```
Cause
Methods of metaclasses like type, e.g. .mro() expect an explicit first argument which is the actual type object being used.
Using
type(or any other subclass oftype, e.g. a custom metaclass) as the type hint for one of the parameters of a function of a multimethod makes the dispatch process raise aTypeErrorwhen callingtype.mro()(which expects the type object as an argument).Example
Expected
Actual
Traceback:
Cause
Methods of metaclasses like
type, e.g..mro()expect an explicit first argument which is the actual type object being used.