sample for habr.ru

MessagedExpressions.py

import unittest
import logging


logging.basicConfig(level = logging.DEBUG)
log = logging.getLogger("messaged.expression")

class MessagedExpression(object):
    def __init__(self, val, msg):
        log.debug("%s evaluated" % val)
        self.msg = msg
        self.val = val

    def __nonzero__(self):
        return self.__bool__()

    def __bool__(self):
        return bool(self.val)


_me = MessagedExpression

def calculate_me():
    log.debug("hardcore calculations")

class Test(unittest.TestCase):


    def test(self):
        result = _me("123","first") and _me(False, "second") and _me(calculate_me(),"calculated")
        self.assertEqual(result.msg,"second")

        result = _me("123","first") and _me(False, "second") or  _me(calculate_me(),"calculated")
        self.assertEqual(result.msg,"calculated")


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