I'm trying to build a command line interface with Python's argparse module. I want two positional arguments where one depends on the other (mutually inclusive). Here is what I want:
prog [arg1 [arg2]]
Here's what I have so far:
prog [arg1] [arg2]
Which is produced by:
parser = argparse.ArgumentParser()
parser.add_argument('arg1', nargs='?')
parser.add_argument('arg2', nargs='?')
How do I get from there to having a mutually inclusive arg2?
Module argparse doesn't have options for creating mutually inclusive arguments.
However it's simple to write it by yourself.
Start with adding both arguments as optional:
parser.add_argument('arg1', nargs='?')
parser.add_argument('arg2', nargs='?')
After parsing arguments check if arg1 is set and arg2 is not:
args = parser.parse_args()
if args.arg1 and not args.arg2:
(this may be more tricky if you change default value from None for not used arguments to something different)
Then use parser.error() function to display normal argparse error message:
parser.error('the following arguments are required: arg2')
Finally change usage: message to show that arg2 depends on arg1:
parser = argparse.ArgumentParser(usage='%(prog)s [arg1 [arg2]]')
A complete script:
import argparse
parser = argparse.ArgumentParser(usage='%(prog)s [arg1 [arg2]]')
parser.add_argument('arg1', nargs='?')
parser.add_argument('arg2', nargs='?')
args = parser.parse_args()
if args.arg1 and not args.arg2:
parser.error('the following arguments are required: arg2')
You can do something similar to this using sub_parsers.
Here are the docs and examples:
