flexible_partial.py

from functools import partial

class FlexiblePartial:
    def __init__(self, func, __varnames=None):
        if not isinstance(func, partial):
            self.__varnames = func.__code__.co_varnames
        else:
            self.__varnames = __varnames
        self.func = partial(func)

    def __call__(self, *args, **kwargs):
        unspecified_varnames = self.__get_unspecified_varnames(args, kwargs)
        if unspecified_varnames:
            return FlexiblePartial(partial(self.func,*args, **kwargs), self.__varnames)
        else:
            return self.func(*args, **kwargs)

    def __repr__(self):
        type_ = type(self)
        brace_pos = str(self.func).find('(')
        return (
            "{module}.{name}{partial_repr_part}"
                .format(
                    module=type_.__module__,
                    name=type_.__qualname__,
                    partial_repr_part=str(self.func)[brace_pos:]
                )
        )

    def __get_unspecified_varnames(self, args, kwargs):
        full_argct = len(self.func.args) + len(args)
        full_argnames = set(self.__varnames[:full_argct])
        full_kwargnames = set(partial(self.func, a=3).keywords.keys()) | set(kwargs.keys())
        unspecified_varnames = set(self.__varnames) ^ (full_argnames | full_kwargnames)
        return unspecified_varnames

##EXAMPLE

@FlexiblePartial
def add_(a, b, c):
    return a + b + c

print(add_)
# __main__.FlexiblePartial(<function add_ at 0x0000000004BCFD08>)

add_23 = add_(2, c=3)
print(add_23)
# __main__.FlexiblePartial(<function add_ at 0x0000000004BCFD08>, 2, c=3)

print(add_23(4))
# 9

print(add_(2)(3,4))
# 9

print(add_(2,3)(4))
# 9

print(add_(2)(3)(4))
# 9