Run python script with some of the argument that are optional

Question

I have gone through the sys documentation, however there is something that is still unclear to me. I have looked for some similar question on stackoverflow, but I h

Answer 1

Other than using argparse (which I do recommend), this can be solved by slicing and expanding:

    sys.exit(example(*sys.argv[1:7]))

The slice will only contain elements that actually exist, even if there aren't enough to fulfill the size of slice requested.

Answer 2

Using Argparse

I suggest you use argparse (and here is the tutorial ). Saves you having to manually check for the existence of parameters. Moreover argparse gives you the --help argument as a freebie, which will read the help="" string defined for each argument, if provided.

Sample Program

In your case you have three mandatory (positional) argument and three optional ones. A sample argparse code would look like this:

#!/usr/bin/python
# coding: utf-8

import argparse

def parseArguments():
    # Create argument parser
    parser = argparse.ArgumentParser()

    # Positional mandatory arguments
    parser.add_argument("creditMom", help="Credit mom.", type=float)
    parser.add_argument("creditDad", help="Credit dad.", type=float)
    parser.add_argument("debtMom", help="Debt mom.", type=float)

    # Optional arguments
    parser.add_argument("-dD", "--debtDad", help="Debt dad.", type=float, default=1000.)
    parser.add_argument("-s", "--salary", help="Debt dad.", type=float, default=2000.)
    parser.add_argument("-b", "--bonus", help="Debt dad.", type=float, default=0.)

    # Print version
    parser.add_argument("--version", action="version", version='%(prog)s - Version 1.0')

    # Parse arguments
    args = parser.parse_args()

    return args

def example(credit_mom, credit_dad, debt_mom, debt_dad = 1000, salary = 2000, bonus = 0):
    total_gain = salary + credit_dad + credit_mom + bonus
    total_loss = debt_dad + debt_mom

    return total_gain - total_loss

if __name__ == '__main__':
    # Parse the arguments
    args = parseArguments()

    # Raw print arguments
    print("You are running the script with arguments: ")
    for a in args.__dict__:
        print(str(a) + ": " + str(args.__dict__[a]))

    # Run function
    print(example(args.creditMom, args.creditDad, args.debtMom, args.debtDad, args.salary, args.bonus))

Answer 3

While I endorse the argparse approach, here's a quick and dirty approach:

arg1, arg2, arg3 = [None, False, []]
if sys.argv[1:]:   # test if there are atleast 1 argument (beyond [0])
    arg1 = sys.argv[1]
    if sys.argv[2:]:
        arg2 = sys.argv[2]  # careful 'True' is a string, not a boolean
        arg3 = sys.argv[3:]  # rest

Mostly I use this when I'm starting to add argument parsing to a script, and my choices of arguments hasn't matured. It's more suited to 'positionals' than 'optionals' (to use argparse terminology).

Answer 4

Your function "example" is just fine. The problem is that you're trying to read sysargs that aren't there. Try to check if they are empty (in the else-clause).