How to handle properly two arguments for one option in python script command line?

Question

I have a "main.py" python script. I want to handle two arguments for one option when I run my script in command line.

For example, I will write the following command in my terminal:

python main.py --interval 2 4

I want to be able to get these 2 arguments (2 and 4) for this specific option (--interval) in my program.

"main.py" program:

from sys import argv
from getopt import getopt, GetoptError


try:
    opts, args = getopt(argv[1:], "i:", ["interval="])
except GetoptError:
    print("usage: main.py --interval <start value> <end value>")
    exit(2)

for opt, arg in opts:
    if opt in ("-i", "--interval"):
        print("Start value: " + arg + ", end value: " + "?")

You can see in the last line of the program, I put a question mark at the place I would get the second argument for the "--interval" option.

The result I want should be:

Start value: 2, end value: 4

I know for this simple example I could just use argv[1] for the option, argv[2] and argv[3] for the arguments. But I would like to know if it is possible to do it with "getopt" library and if yes, if it is the proper way to do it.

Have you considered using argparse? "Users who are unfamiliar with the C getopt() function or who would like to write less code and get better help and error messages should consider using the argparse module instead." — jonrsharpe
– jonrsharpe, Commented Mar 26, 2017 at 14:54
Thanks to this thread, I'm definitely going to take a long look at argparse. However, if you are devoted to using getopt, you should know that an option takes at most one argument. So, you could cheat if you really wanted to move on quickly ( read that as, you don't care about quality ) . The cheat in this case is passing the interval as a space delimited string. This is tough on operators, but they could run your program as: program.py --interval="2 4". Of course, your code would have to split the option. You would also need to have suitable documentation. — Mark
– Mark, Commented Mar 26, 2017 at 15:05
@Mark, I generally use argparse pretty successfully for parsing this stuff so I haven't tried anything else. However, I've heard good things about click, and Google recently open sourced python-fire. You might want to try them if argparse doesn't scratch your itch. — Ben
– Ben, Commented Mar 26, 2017 at 15:10

Ben · Accepted Answer · 2017-03-26 14:55:21Z

1

The argparse module in the standard library has an example just like this:

import argparse

parser = argparse.ArgumentParser(description='Process some integers.')
parser.add_argument('integers', metavar='N', type=int, nargs='+',
                    help='an integer for the accumulator')
parser.add_argument('--sum', dest='accumulate', action='store_const',
                    const=sum, default=max,
                    help='sum the integers (default: find the max)')

args = parser.parse_args()
print(args.accumulate(args.integers))

In your example, you can simply replace the nargs='+' argument with nargs=2. Doing that produces the following usage message on my terminal (pass the -h flag to get usage):

usage: tmp.py [-h] [--sum] N N

answered Mar 26, 2017 at 14:55

Ben

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