Minglish | Python Fiddle

def answer(words):
    alphabet = []
    rules = []
    word_count = len(words)
    default_rule = ['1','1']

def get_word_rules(word1, word2):
        length = min(len(word1), len(word2))
        print "comparing %s and %s" % (word1, word2)
        for x in range(length):
            if word1[x] != word2[x]:
                print "rule = %s, %s" % (word1[x], word2[x])
                return [str(word1[x]), str(word2[x])]
        print "rule = %s, %s" % (1, 1)
    	return default_rule
            
    # Find the rule that contains a letter that is never on the right
    # This is the first letter
    def find_first_letter():
    	length = len(rules)
        less_than_list = set()
        greater_than_list = set()
    	for rule in rules:
            less_than_list.update(rule[0])
            greater_than_list.update(rule[1])
                
        #print less_than_list
        #print greater_than_list
        return (less_than_list - greater_than_list).pop(),(greater_than_list - less_than_list).pop()
    
    for index in range(word_count - 1):
        rule = get_word_rules(words[index], words[index+1])
        if rule is not default_rule and rule not in rules:    
            rules.append(rule)

print "Rules list %s" % rules

while len(rules) > 1:
    
        left_edge, right_edge = find_first_letter()
        print "left edge =%s" % left_edge
        print "Rules list %s" % rules
        old_rules = rules
    	for rule in old_rules:
            # print rules
            print 'Testing rule %s' % rule
            if rule[0] == left_edge or rule[1] == right_edge:
            	rules.remove(rule)

alphabet_left.append( left_edge )
        alphabet_right.insert(0, right_edge )
	alphabet = alphabet_left + alphabet_right
    alphabet.append(rules[0][0])
    if rules[0][1] not in alphabet:
    	alphabet.append(rules[0][1])
    return alphabet

words = ["ba", "ab", "cb"]
# words = ["z", "yx", "yz", "az", "ay", "baz", "bay"] 
words = ["z", "yx", "yz", "az","az", "ay", "baz", "bay"] 
words = ['c', 'cac', 'cb', 'bcc', 'ba'] # cab
words = ['c', 'cac', 'cb', 'cz', 'bcc', 'ba'] # cabz
print answer(words)

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