>>> 대문자 = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
>>> 소문자 = "abcdefghijklmnopqrstuvwxyz"
>>> 숫자 = "0123456789"
>>> s = "p0Y123!@#THon"
>>> s_u, s_l, s_n, s_s = "", "", "", ""
>>> for c in s:
    if c in 대문자:
        s_u += c
    elif c in 소문자:
        s_l += c
    elif c in 숫자:
        s_n += c
    else:
        s_s += c


>>> s_u, s_l, s_n, s_s
('YTH', 'pon', '0123', '!@#')
>>> len(s_u), len(s_l), len(s_n), len(s_s)
(3, 3, 4, 3)

string 모듈에 소문자, 대문자, 숫자등이 정의되어 있습니다.

>>> s = 'p0Y123!@#THon'
>>> import string
>>> string.digits
'0123456789'
>>> string.ascii_lowercase
'abcdefghijklmnopqrstuvwxyz'
>>> string.ascii_uppercase
'ABCDEFGHIJKLMNOPQRSTUVWXYZ'
>>> list(filter(lambda c:c in string.ascii_lowercase, s))
['p', 'o', 'n']

파이썬의 기본모듈을 사용하면 반복구조를 만들필요가 없습니다.

import itertools as it
import string
from collections import Counter

classification_char_type = lambda c: 'lower' if c in string.ascii_lowercase else 'upper' if c in string.ascii_uppercase else 'digit' if c in string.digits else 'special'

s = 'p0Y123!@#THon'
counter = Counter(list(iter(lambda s=iter(s): classification_char_type(next(s)), [])))
print(counter)

Counter({'digit': 4, 'lower': 3, 'upper': 3, 'special': 3})