pattern calculator

def createPatternDictionary(pattern):
    rules = {1: ('...', '.'), 2: ('..x', '.'), 4: ('.x.', '.'), 8: ('.xx', '.'),
             16: ('x..', '.'), 32: ('x.x', '.'), 64: ('xx.', '.'), 128: ('xxx', '.')}
    left = pattern
    for i in sorted(rules.keys(), reverse=True):
        if left - i >= 0:
            left = left - i
            rules[i] = rules[i][0], 'x'
    return rules