''' Solution to Problem 7.  '''

# k and v are lists
def make( k, v ) :

    if (len(k) != len(v)):
        return None
    # It must be the case that the 2 lists are the same length
    new_dict = {}
    for i in range(0, len(k)):
        k_value = k[i] # This will be the new key
        v_value = v[i] # This will be the new value
        new_dict[k_value] = v_value
        # We have now added this key to the dictionary and mapped it to the value

    return new_dict

# d is a dictionary
def onto( d ) :
    # This function will return true if all the values in the dictionary are unique
    v = d.values()
    v = set(v) # set() returns a set with only one copy of each thing in the original v

    k = d.keys() # This returns an iterable object of all the keys in the dictionary

    if (len(v) == len(k)):
        # If v is still the same length, then all the values were unique in the first place
        return True
    else:
        return False


if ( __name__ == '__main__' ) :
    
    try :
        d1 = make( [1, 2, 3], [ 'a', 'b', 'c', 'd'  ] )
        d2 = make( [1, 2, 3, 4], [ 'a', 'b', 'c', 'd'  ] )
        print( d1 )
        print( d2 )
    except :
        print( 'make() blows up' )

    try :
        b1 = onto( { 1: 'odd', 2: 'even', 3: 'prime' } )
        b2 = onto( { 1: 'odd', 2: 'even', 3: 'odd' } )
        print( b1, b2 )
    except :
        print( 'surjection() blows up' )