Python-сообщество

import re
string = "abc a bCd bC AbC BC BCD bcd ABC abc bcd bcd abc"
string = string.lower()
spisok = re.findall(r'\w+', string)
dic = {}
for i in spisok:
    if i in dic:
        dic[i] += 1
    else:
        dic[i] = 1
print(*min(keys for keys in dic.items() if keys[1] == max(dic.values())))
print(dic)

print(*min(keys for keys in dic.items() if keys[1] == max(dic.values())))

>>> t = ('c', 10000)
>>> print(*t)
c 10000
>>>