Functional version of the Python */** operators

star.py

# -*- coding: utf-8 -*-
#
# Author: Ian Eure <ian@digg.com>
#

"""Star function."""

from functools import partial
import unittest

def star(f, *args, **kwargs):
    """Return a function which works like the * operator.

    This is a mix of partial application and the * / ** operator
    (e.g. apply). When called with a function and arguments, returns a
    function with arguments partially applied, which accepts further
    arguments supplied in a sequence, dict, or both.

    e.g.

    star(f, 1, 2)() -> f(1, 2)
    star(f, 1)((2, 3)) -> f(1, 2 ,3)
    star(f)((1, 2)) -> f(1,2)
    star(f)({'a': 1, 'b':2}) = f(a=1, b=2)

    If you supply one non-sequence argument, it will do the right thing:
    star(f, 1)(2) -> f(1, 2)

    It's useful for applying dicts or sequences as function arguments:

    map(star(f), {'a': 1, 'b': 2}.items()) -> (f(a=1), f(b=2))
    """
    f = partial(f, *args, **kwargs)
    def __inner__(args = None, kwargs = None):
        if isinstance(args, dict):
           _kwargs = args
           if kwargs:
               _kwargs.update(kwargs)
               kwargs = None
           kwargs = _kwargs
           args = None

        if args != None and not \
                (isinstance(args, tuple) or isinstance(args, list)):
            args = (args,)

        args = args or ()
        kwargs = kwargs or {}
        return f(*args, **kwargs)

    return __inner__


def _bar(a, b, c=None):
    if c:
        return "%s%s%s" % (a, b, c)
    return "%s%s" % (a, b)

class TestStar(unittest.TestCase):
    def _foo(self, a, b, c=None):
        return _bar(a, b, c)

    def test_star_plain(self):
        for f in (self._foo, _bar):
            f_ = star(f)
            self.assert_(f_((1, 2)) == "12")
            f_ = star(f, 1)
            self.assert_(f_((2,)) == "12")
            f_ = star(f, 1, 2)
            self.assert_(f_({'c': 3}) == "123")
            f_ = star(f, 1)
            self.assert_(f_(2) == "12")


if __name__ == '__main__':
    unittest.main()