Python-сообщество

while True:
    s = input("").replace(" ", "")
    [exit("Error") for i in s if i not in list(map(str, range(10)))+['+', '-', '*', '/', '%', '**']]
    print(eval(s))

actions = ('+', '-', '*', '/', '%', '**')
while True:
    string = raw_input('')
    args = string.split(' ')
    if string == 'exit':
        print('bye')
        break
    elif len(args) == 3:
        if isinstance(args[0], int) and isinstance(args[2], int) and args[1] in actions:
            print(eval(string))
        else:
            print('error')
            break
    else:
        print('error')
        break

while True:
    e = input().lower() # if python 2.x: e = raw_input().lower()
    if e == 'exit':
        print('bye')
        break
    lst = e.split()
    if len(lst) != 3 or \
        not lst[0].isdigit() or \
        lst[1] not in ['+', '-', '*', '/', '%', '**'] or \
        not lst[2].isdigit():
            print('error')
            break
    try:
        result = eval(e)
    except Exception as err: # if python 2.x: except Exception, err:
        result = err
    print(result)
        

-2 - 3
error

while True:
    e = input().lower().strip()
    if e == 'exit':
        print('bye')
        break
    lst = e.split()
    try:
        assert len(lst) == 3 and \
            lst[1] in ['+', '-', '*', '/', '%', '**'] and \
            isinstance(eval(lst[0]), int) and \
            isinstance(eval(lst[2]), int)
        print(eval(e))
    except ZeroDivisionError:
        print('Zero division')
    except Exception:
        print('error')
        break