IndexError: list index out of range when no argument is supplied

Question

I just want to know why this code is generating IndexError: list index out of range when no argument supplied to it?

script.py

import sys
a = sys.argv[1]
print(a)

Sample output with argument/s

user@linux:~$ python3 script.py abc
abc
user@linux:~$ python3 script.py abc def
abc
user@linux:~$

Sample output without argument/s

user@linux:~$ python3 script.py
Traceback (most recent call last):
  File "script.py", line 2, in <module>
    a = sys.argv[1]
IndexError: list index out of range
user@linux:~$

My reference: https://www.pythonforbeginners.com/system/python-sys-argv

Answer 1

From the python docs sys.argv returns:

The list of command line arguments passed to a Python script. argv[0] is the script name (it is operating system dependent whether this is a full pathname or not).

The problem is that when you run your script without arguments like python3 script.py, you are trying to access the element at index 1 by using sys.argv[1] but in fact this element doesn't even exists in the list. Therefore, The python interpreter throws an IndexError.