PythonLanguage doesn't have interfaces like JavaInterface''''''s. If it's for MultipleInheritance, Python already has it, but for "contract compliance" it hasn't.

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Not built-in, but ZopeApplicationServer has an 'interfaces' module that does pretty much everything you could want. The Twisted framework for AsynchronousProgramming also has a usable implementation of interfaces as regards contract compliance. -- MoeAboulkheir

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There is a PEP for implementing Interface Syntax in Python. It's PEP-245 at http://www.python.org/peps/pep-0245.html.

It would be very nice when it's implemented, but it still can't guarantee the semantics (pre/post-conditions, and invariants) even if it's implemented. Yes, you should follow the documentation very carefully. If you are a good programmer it won't be any problem but if you are a rogue or novice programmer, what happens? ''If you're a rogue programmer, your code is going to stink anyway. If you're a novice, what are you doing bungling around with interfaces?''

I do use UnitTest''''''s extensively when programming and apply them to interfaces compliance checking as well.

You know interfaces sometimes can deceive you -- it could be fictitious without semantic guarantee. With UnitTest''''''s, however, the interfaces can guarantee semantics as well.

The following code will tell, (If the client implements Stack''''''Interface with List''''''Stack, she'll make a unittest module for that and name it "test_StackList". In the test, she just imports all the tests from Stack''''''Interface so that interface compliances are guaranteed. She might add some List''''''Stack-specific test cases in the same module test_StackList.)

        #------------------------------------------------
        #Stack''''''Interface.py
        import unittest

        class Stack''''''Interface:  #or put this whole class as a doc string
            '''Anything that implements this should pass the unittests in
               Stack''''''Interface with its own My''''''Impl
            '''
            def push(self, anObject):
                raise NotImplementedE''''''rror
            def pop(self):
                raise NotImplementedE''''''rror
            def isEmpty(self):
                raise NotImplementedE''''''rror

        class _Object: #helper object representing _anything_
            pass

        class TestStackI''''''nterface(unittest.TestCase):
            def setUp(self):
                self.stack=My''''''Impl()
            def testPushAndPop(self):
                o=_Object()
                self.stack.push(o)
                self.assertEqual(o, self.stack.pop())
            def testPopOnEmpty(self):
                self.assert_(self.stack.isEmpty())
                self.assertRaises(Index''''''Error,self.stack.pop)
            def testPushAllAndPopAll(self):
                oList=[_Object() for i in range(10)]
                for each in oList:
                    self.stack.push(each)
                oList.reverse()
                for each in oList:
                    self.assertEqual(each, self.stack.pop())

        My''''''Impl=Stack''''''Interface #please override this with the real implementation

        if __name__=='__main__':  # you won't run this module directly though
            unittest.main()

        #------------------------------------------------
        #List''''''Stack.py
        from Stack''''''Interface import Stack''''''Interface
        class List''''''Stack(Stack''''''Interface):
            def __init__(self):
                self._s=[]
            def push(self, anObject):
                self._s.append(anObject)
            def pop(self):
                return self._s.pop()
            def isEmpty(self):
                return len(self._s)==0

        #------------------------------------------------
        #test_ListStack.py
        import unittest

        import Stack''''''Interface
        from List''''''Stack import List''''''Stack
        Stack''''''Interface.My''''''Impl=List''''''Stack

        from Stack''''''Interface import *  #if you want to implement several
                                      #interfaces just import all of them here
        if __name__=='__main__':
            unittest.main()
-- JuneKim

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CategoryInterface CategoryPython