Python 使用list实现简单的map

# An map iterator
class _MapIterator:
    def __init__(self, theList):
        self._mapItems = theList
        self._curItem = 0

    def __iter__(self):
        return self

    def next(self):
        if self._curItem < len(self._mapItems):
            item = self._mapItems[self._curItem]
            self._curItem += 1
            return item
        else:
            raise StopIteration

# Implementation of Map ADT using a single list
class myMap:
    # Creates an empty map instance
    def __init__(self):
        self._entryList = list()

    # Returns the number of entries in the map
    def __len__(self):
        return len(self._entryList)

    # Determines if the map contains the given key
    def __contains__(self, key):
        ndx = self._findPosition(key)
        return ndx is not None

    # Adds a new entry to the map if the key does exist. 
    # Otherwise, the new value replaces the current value associated with the key
    def add(self, key, value):
        ndx = self._findPosition(key)
        if ndx is not None:
            self._entryList[ndx].value = value
            return False
        else:
            entry = _MapEntry(key, value)
            self._entryList.append(entry)
            return True

    # Returns the value associated with the key
    def valueOf(self, key):
        ndx = self._findPosition(key)
        assert ndx is not None, "Invalid map key."
        return self._entryList[ndx].value

    # Removes the entry associated with the key
    def remove(self, key):
        ndx = self._findPosition(key)
        assert ndx is not None, "Invalid map key."
        self._entryList.pop(ndx)

    # Returns an iterator for traversing the keys in the map
    def __iter__(self):
        return _MapIterator(self._entryList)

    # Helper method used to find the index position of a category
    # If the key is not found, None is returned
    def _findPosition(self, key):
        # Iterate through each entry in the list
        for i in range(len(self)):
            # Is the key stored in the ith entry?
            if self._entryList[i].key == key:
                return i
        # when not found, return None
        return None

# Storage class for holding the key/value pairs
class _MapEntry:
    def __init__(self, key, value):
        self.key = key
        self.value = value  

def test_linearmap():
    
    # import mySet
    from linearmap import myMap
    
    # init a set named smith
    smith = myMap()
    smith.add('name', 'beyond')
    smith.add('value', 'nihao')
        
    for a in smith:
        print "key:%s value:%s" % (a.key, a.value)
        
if __name__ == "__main__":
    test_linearmap()