def levenshtein_distance_metric ( a , b ) : return ( levenshtein_distance ( a , b ) / ( 2.0 * max ( len ( a ) , len ( b ) , 1 ) ) )
python levenshtein distance performance
1 - farthest apart ( same number of words all diff ) . 0 - same
def levenshtein_distance_metric(a, b):
    """ 1 - farthest apart (same number of words, all diff). 0 - same"""
    return (levenshtein_distance(a, b) / (2.0 * max(len(a), len(b), 1)))