Parsing command line input for numbers

Question

I'm writing a command line application and would like the user to be able to enter numbers as individual numbers or as a range. So, for example:

$ myapp -n 3,4,5,6

or

$ myapp -n 3-6

I would like my app to put these into a Python list e.g., [3, 4, 5, 6] I'm using optparse, but am not sure how to create the list from these two styles of inputs. Some example code would be great.

EDIT

I would like to be able to enter multiple ranges too:

$ myapp -n 22-27, 51-64

Answer 1

import argparse

def parse_range(astr):
    result = set()
    for part in astr.split(','):
        x = part.split('-')
        result.update(range(int(x[0]), int(x[-1]) + 1))
    return sorted(result)

parser = argparse.ArgumentParser()
parser.add_argument('-n', type=parse_range)
args = parser.parse_args()
print(args.n)

yields

% script.py -n 3-6
[3, 4, 5, 6]

% script.py -n 3,6
[3, 6]

% script.py -n 22-27,51-64 
[22, 23, 24, 25, 26, 27, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64]