How to adjust Python's sys.argv to change its length accordingly

I've been attempting to make the sys.argv[] to either change its output according to the number of argument that the user input. I am trying to make it so that if there is no sys.argv[5] then it would use sys.argv[4]. Currently I have tried both this ideas with my problem always IndexError: list index out of range when I do attempt to make sys.argv[5] left empty:

if len(sys.argv) is 4:
    location = int(sys.argv[1])
    order = sys.argv[2]
    amount = sys.argv[3]
    user = sys.argv[4]
    company= sys.argv[4]
    print(company)
else:
    location = int(sys.argv[1])
    order = sys.argv[2]
    amount = sys.argv[3]
    user = sys.argv[4]
    company= sys.argv[5]
    print(company)

also attempted to change "if len(sys.argv) is 4:" with "if sys.argv[5] != True:". I've read some posting about solving the index but just don't know how to actually tailor the code for my own use.

Thanks!