Python 使用list实现简单的set

# Implementation of iterclass _SetIterator:    def __init__(self, theList):        self._setItems = theList        self._curItem = 0    def __iter__(self):        return self    def next(self):        if self._curItem < len(self._setItems):            item = self._setItems[self._curItem]            self._curItem += 1            return item        else:            raise StopIteration        # Implementation of the Set ADT container using a Python listclass mySet:    # Creates an empty set instance    def __init__(self):        self._theElements = list()    # Returns the number of items in the set    def __len__(self):        return len(self._theElements)    # Determines if an element is in the set    def __contains__(self, element):        return element in self._theElements    # Adds a new unique element to the set    def add(self, element):        if element not in self:            self._theElements.append(element)    # Removes an element from the set    def remove(self, element):        assert element in self, "The element must be in the set."        self._theElements.remove(element)    # Determines if two sets are equal    def __eq__(self, setB):        if len(self) != len(setB):            return False        else:            return self.isSubsetOf(setB)    # Determines if this set is a subset of setB    def isSubsetOf(self, setB):        for element in self:            if element not in setB:                return False        return True    # Creates a new set from the union of this set and setB    def union(self, setB):        newSet = mySet()        newSet._theElements.extend(self._theElements)        for element in setB:            if element not in self:                newSet._theElements.append(element)        return newSet    # Creates a new set from the intersection    def interset(self, setB):        newSet = mySet()        for element in setB:            if element in self:                newSet._theElements.append(element)        return newSet    def difference(self, setB):        newSet = mySet()        for element in self:            if element not in setB:                newSet._theElements.append(element)        return newSet    # Returns an iterator for traversing the list of items    def __iter__(self):        return _SetIterator(self._theElements)

def test_linearset():        # import mySet    from linearset import mySet        # init a set named smith    smith = mySet()    smith.add('CSCI-112')    smith.add('MATH-121')    smith.add('HIST-340')    smith.add('ECON-101')        # init a set named roberts    roberts = mySet()    roberts.add('POL-101')    roberts.add('ANTH-230')    roberts.add('CSCI-112')    roberts.add('ECON-101')        for a in smith:        print a                if __name__ == "__main__":    test_linearset()