defer.py

class Defer(object):
    """ Defer is the idea stolen from golang. Instead of calling a function
    immediately, it defers running the function by saving it to a list. The
    saved list of functions get executed when the surrounding function returns.
    """

    def __init__(self):
        self.funcs = []

    def defer(self, func, args=()):
        self.funcs.append((func, args))

    def run(self):
        for f in reversed(self.funcs):
            f[0](*f[1])

test_defer.py

import unittest

from hamcrest import *  # noqa
from matchers import *  # noqa
from mock import MagicMock

from common.defer import Defer


class TestDefer(unittest.TestCase):

    def test_defer(self):
        d = Defer()

        f1 = MagicMock()
        f2 = MagicMock()
        f3 = MagicMock()

        d.defer(f1, (1,2,3))
        d.defer(f2, (1,))
        d.defer(f3)

        d.run()

        f1.assert_called_once_with(1,2,3)
        f2.assert_called_once_with(1,)
        f3.assert_called_once_with()

    def test_defer_order(self):
        d = Defer()

        order = []
        def f1():
            order.append("f1")

        def f2():
            order.append("f2")

        d.defer(f1)
        d.defer(f2)

        d.run()

        assert_that(order, equal_to(["f2", "f1"]))