Question

import sys

def Hello(name):
   name = name + '!!!'
   print 'Hello' ,  name


def main():
    Hello(sys.argv[1])


if __name__ == '__main__':
       main()

Here is the error

Traceback (most recent call last):
  File "D:\pythonPractice\firstPython.py", line 13, in <module>
    main()
  File "D:\pythonPractice\firstPython.py", line 9, in main
    Hello(sys.argv[1])
IndexError: list index out of range

I have also tried sys.argv[2] but error remains

Answer 1

First things first, I think the code you originally posted (with Hello(sys.argv[0])) is not what you actually have. It doesn’t match the error, which states sys.argv[1], so what you probably have is:

def main():
    Hello(sys.argv[1])

As to the error then, it’s because you haven’t provided an argument when running. You need to do so, such that sys.argv[1] exists:

python helloprog Pax

You would find a more robust main as:

def main():
    if len(sys.argv) < 2:
        Hello("whoever you are")
    else:
        Hello(sys.argv[1])

which will detect when you haven’t provided an argument, and use a suitable default rather than raising an exception.