How to use python argparse with args other than sys.argv?


Is there a way to use argparse with any list of strings, instead of only with sys.argv?

Here’s my problem: I have a program which looks something like this:

# This file is
import argparse

def main(argv):
    parser = argparse.ArgumentParser()
    # Do some argument parsing

if __name__ == '__main__':

This works fine when this program is called straight from the command line. However, I have another python script which runs batch versions of this script with different commandline arguments, which I’m using like this:

import program1

arguments = ['arg1', 'arg2', 'arg3']

I still want to be able to parse the arguments, but argparse automatically defaults to using sys.argv instead of the arguments that I give it. Is there a way to pass in the argument list instead of using sys.argv?

Asked By: ClydeTheGhost



Just change the script to default to sys.argv[1:] and parse arguments omitting the first one (which is the name of the invoked command)

import argparse,sys

def main(argv=sys.argv[1:]):
    parser = argparse.ArgumentParser()
    parser.add_argument("--level", type=int)
    args = parser.parse_args(argv)

if __name__ == '__main__':

Or, if you cannot omit the first argument:

import argparse,sys

def main(args=None):
    # if None passed, uses sys.argv[1:], else use custom args
    parser = argparse.ArgumentParser()
    parser.add_argument("--level", type=int)
    args = parser.parse_args(args)

    # Do some argument parsing

if __name__ == '__main__':

Last one: if you cannot change the called program, you can still do something

Let’s suppose the program you cannot change is called (I added a call to print arguments)

Then just change the local argv value of the argtest.sys module:

import argtest


['dummy', 'foo', 'bar']    

You can pass a list of strings to parse_args:

parser.parse_args(['--foo', 'FOO'])
Answered By: iCart

Python argparse now has a parameter nargs for add_argument (https://docs.python/3/library/argparse.html).

It allows us to have as many arguments as we want for a named parameter (here, alist)

import argparse
parser = argparse.ArgumentParser()
parser.add_argument("--alist", nargs="*")
args = parser.parse_args()


All command line values that follow --alist are added to a list.


$ python3 --alist fred barney pebbles "bamm bamm"
['fred', 'barney', 'pebbles', 'bamm bamm']

As you see, it is allowed to quote the arguments, but not necessary unless you need to protect a space.

Answered By: pauljohn32
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