Getting IndexError when trying to use default function arguments, if no commandline arguments are passed to script

Question

I'm having some issues with some python logic. Not sure if that's possible but if it's possible with bash I guess that's possible in every other language.

I want to use default function argument if no commandline argument is passed to script:

#!/usr/bin/env python3

import sys

def get_file_name(filename: str = "watched_movies"):
    if sys.argv[1]:
        filename = sys.argv[1]
        return filename
    return filename
    
print(get_file_name())

My code might be wrong because I was just doing some poking around.

I'm getting error:

Traceback (most recent call last):
  File "/home/os/scripts/python/./movies.py", line 11, in <module>
    print(get_file_name())
  File "/home/os/scripts/python/./movies.py", line 6, in get_file_name
    if sys.argv[1]:
IndexError: list index out of range

Answer 1

Try it:

#!/usr/bin/env python3
    
import sys

def get_file_name(filename: str = "watched_movies"):
    if len(sys.argv) > 1 and sys.argv[1]:
        filename = sys.argv[1]
        return filename
    return filename 
    
print(get_file_name())

In a single line:

def get_file_name(filename: str = "watched_movies"):
    return filename if len(sys.argv) == 1 else sys.argv[1]