How to use the multimethod.__init__.multimethod function in multimethod

docs = []
        for func in set(self.values()):
            try:
                sig = inspect.signature(func)
            except ValueError:
                sig = ''
            doc = func.__doc__ or ''
            docs.append(f'{func.__name__}{sig}\n    {doc}')
        return '\n\n'.join(docs)


class multidispatch(multimethod):
    """Provisional wrapper for future compatibility with `functools.singledispatch`."""


get_type = multimethod(type)
get_type.__doc__ = """Return a generic `subtype` which checks subscripts."""
for atomic in (Iterator, str, bytes):
    get_type[atomic,] = type


@multimethod  # type: ignore[no-redef]
def get_type(arg: tuple):
    """Return generic type checking all values."""
    return subtype(type(arg), *map(get_type, arg))


@multimethod  # type: ignore[no-redef]
def get_type(arg: Mapping):
    """Return generic type checking first item."""
    return subtype(type(arg), *map(get_type, next(iter(arg.items()), ())))

def __setitem__(self, key, value):
            if callable(value):
                value = getattr(self.get(key), 'register', multimethod)(value)
            super().__setitem__(key, value)

@multimethod  # type: ignore[no-redef]
def get_type(arg: tuple):
    """Return generic type checking all values."""
    return subtype(type(arg), *map(get_type, arg))

    @property
    def docstring(self):
        """a descriptive docstring of all registered functions"""
        docs = []
        for func in set(self.values()):
            try:
                sig = inspect.signature(func)
            except ValueError:
                sig = ''
            doc = func.__doc__ or ''
            docs.append(f'{func.__name__}{sig}\n    {doc}')
        return '\n\n'.join(docs)


class multidispatch(multimethod):
    """Provisional wrapper for future compatibility with `functools.singledispatch`."""


get_type = multimethod(type)
get_type.__doc__ = """Return a generic `subtype` which checks subscripts."""
for atomic in (Iterator, str, bytes):
    get_type[atomic,] = type


@multimethod  # type: ignore[no-redef]
def get_type(arg: tuple):
    """Return generic type checking all values."""
    return subtype(type(arg), *map(get_type, arg))


@multimethod  # type: ignore[no-redef]