hash table implementation

# Questions: input type, range
# Optimizations: better hash function based on expected inputs (otherwise a big linked list)


class HashTable( object ):
    """ of U possible values our hash function should map to K possible spaces
    """

    def __init__( self ):   # TODO: max? , chaining
        self.MAX = 20       # whenever MAX items are inserted the load is 1 (n/k)
        self.table = [None] * self.MAX


    def put( self, key, value ):    # TODO: hash function
        hash = self.myhash( key )
        chain = self.table[ hash ]
        if chain:
            chain.append( value )       # TODO: FIFO vs LIFO?
            self.table[ hash ]= chain
        else:
            chain = list()
            chain.append( value )
            self.table[ hash ]= chain


    def lookup( self, key ):
        hash = self.myhash( key )
        chain = self.table[ hash ]
        if chain:
            return chain[ 0 ]
        else:
            return None     # raise an Exception?


    def remove( self, key ):
        hash = self.myhash( key )
        chain = self.table[ hash ]
        if chain:
            chain.pop()     # TODO: FIFO vs LIFO?
        else:
            return None     # raise an Exception?


    def myhash( self , key ):
        sum = 0
        for i in xrange( len( key ) ):
            sum += ord( key[ i ] )      # chr( 97 ) returns 'a'  # 256 value limit (extended ascii), unichr()
        hash = sum % self.MAX
        return hash


if __name__ == '__main__':
    h = HashTable()     # print h.table
    retrieved = h.lookup( 'a' )
    print retrieved, "FROM h.lookup( 'a' )  "
    print "INSERTED 'a'"
    h.put( 'a', 'a' )
    retrieved = h.lookup( 'a' )
    print retrieved, " FROM h.lookup( 'a' ) "
    retrieved = h.lookup( 'z' )
    print retrieved, " FROM h.lookup( 'z' ) "

    h.remove( 'a' )
    retrieved = h.lookup( 'a' )
    print retrieved, " FROM h.lookup( 'a' ) AFTER h.remove('a')"

    h.put( 'baza', 'baza' )
    h.put( 'abaz', 'abaz' )
#   print h.table
    retrieved = h.lookup( 'zaab' )
    print retrieved, "FROM h.lookup( 'zaab' ) AFTER INSERTED 'baza' , 'abaz'    "
    h.remove( 'baza' )
    retrieved = h.lookup( 'baza' )
    print retrieved, " FROM h.lookup( 'baza' ) AFTER h.remove( 'baza' ),   (i.e. removed hash collision abaz)"
#   print h.table
    h.remove( 'aazb' )
    retrieved = h.lookup( 'baza' )
    print retrieved, " FROM h.lookup( 'baza' ) AFTER h.remove( 'aazb' ),  (i.e. key that creates hash collision removes the last from the chain)"