WEB Работа с командной строкой ---> Калькулятор 2.0

import sys
a = 0
i = 1
c = 1
while True:
    try:
        a += c * int(sys.argv[i])
        if c == 1:
            c = -1
        else:
            c = 1
    except IndexError:
        if i == 1:
            print('NO PARAMS')
            exit(0)
        break
    except ValueError:
        print('ValueError')
        exit(0)
    i += 1
print(a)