enter = input()
def test(str_):
    if str_.isalpha():
        if str_.isupper() or str_.islower():
            return 1
        else:
            return 0
    else:
        return -1
print(test(enter))

  
>>> def test_two_chars(chars):
...     if not len(chars) == 2:
...         raise ValueError('Expecting two characters')
...     ch1, ch2 = chars
...     if not ch1.isalpha() and not ch2.isalpha():
...         return -1
...     if (ch1.isupper() and ch2.isupper()) or \
...        (ch1.islower() and ch2.islower()):
...         return 1
...     if (ch1.isupper() and ch2.islower()) or \
...        (ch1.islower() and ch2.isupper()):
...         return 0
...     raise ValueError('Unexpected characters')
... 
>>> def f():
...     chars = input('Введите два символа: ')
...     out = test_two_chars(chars)
...     print(out)
... 
>>> f()
Введите два символа: 12
-1
>>> f()
Введите два символа: ab
1
>>> f()
Введите два символа: AB
1
>>> f()
Введите два символа: aB
0
>>> f()
Введите два символа: a1
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<stdin>", line 3, in f
  File "<stdin>", line 13, in test_two_chars
ValueError: Unexpected characters
>>>