CheckIO. The most wanted letter bug.

Error.py

def checkio(text):
	def checkEqual(lst):
		return lst[1:] == lst[:-1]
	counted = {}
	text = text.lower()
	for i in text:
		if i not in counted:
			if i.isalpha():
				counted[i] = text.count(i)
			else:
				counted[i] = -1
	if checkEqual(counted.values()):
		return min(counted)
	else:
		return max(counted, key=counted.get)


if __name__ == '__main__':
	assert checkio(u"fdbbss") == "b", "fdbbss!=b"

Good.py

def checkio(text):
    counted = {}
    text = text.lower()
    for i in text:
        counted[i] = counted.get(i, 0 if i.isalpha() else -1000000) + 1
        
    val = max(counted.values())
    freq = [k for (k, v) in counted.items() if v == val]
    return min(freq)


if __name__ == '__main__':
    assert checkio(u"fdbbss") == "b", "fdbbss!=b"