Experiments with Elixir inspired pipe API for python

pipe.py

import unittest

class Pipe:
    OUT = object()

    def __init__(self, val):
        self._val = val

    def __call__(self, *args):
        if not (args):
            return self._val
        fun = args[0]
        fun_args = []
        has_out = False
        for arg in args[1:]:
            if arg is Pipe.OUT:
                has_out = True
                fun_args.append(self._val)
            else:
                fun_args.append(arg)
        if not has_out:
            fun_args.append(self._val)
        self._val = fun(*fun_args)
        return self

def times2(x):
    return x * 2

def sub(a, b):
    return a - b

class PipeTest(unittest.TestCase):

    def test_pipe(self):
        self.assertEqual(12,
                         Pipe(3)(times2)(times2)())

    def test_call_with_argument(self):
        self.assertEqual([2, 6, 8], Pipe([1,3,4])(map, times2)())

    def test_explicit_position(self):
        self.assertEqual(-9, Pipe(1)(sub, Pipe.OUT, 10)())

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