Python calling a module that uses argparser

Question

This is probably a silly question, but I have a python script that current takes in a bunch of arguments using argparser and I would like to load this script as a module in another python script, which is fine. But I am not sure how to call the module as no function is defined; can I still call it the same way I do if I was just invoking it from cmd?

Here is the child script:

import argparse as ap
from subprocess import Popen, PIPE

parser = ap.ArgumentParser(
    description='Gathers parameters.')
parser.add_argument('-f', metavar='--file', type=ap.FileType('r'), action='store', dest='file',
                    required=True, help='Path to json parameter file')
parser.add_argument('-t', metavar='--type', type=str, action='store', dest='type',
                    required=True, help='Type of parameter file.')
parser.add_argument('-g', metavar='--group', type=str, action='store', dest='group',
                    required=False, help='Group to apply parameters to')
# Gather the provided arguments as an array.
args = parser.parse_args()

... Do stuff in the script

and here is the parent script that I want to invoke the child script from; it also uses arg parser and does some other logic

from configuration import parameterscript as paramscript

# Can I do something like this?
paramscript('parameters/test.params.json', test)

Inside the configuration directory, I also created an init.py file that is empty.

marc_s · Accepted Answer · 2022-07-28 20:28:02Z

42

The first argument to parse_args is a list of arguments. By default it's None which means use sys.argv. So you can arrange your script like this:

import argparse as ap

def main(raw_args=None):
    parser = ap.ArgumentParser(
        description='Gathers parameters.')
    parser.add_argument('-f', metavar='--file', type=ap.FileType('r'), action='store', dest='file',
                        required=True, help='Path to json parameter file')
    parser.add_argument('-t', metavar='--type', type=str, action='store', dest='type',
                        required=True, help='Type of parameter file.')
    parser.add_argument('-g', metavar='--group', type=str, action='store', dest='group',
                        required=False, help='Group to apply parameters to')
    # Gather the provided arguments as an array.
    args = parser.parse_args(raw_args)
    print(vars(args))


# Run with command line arguments precisely when called directly
# (rather than when imported)
if __name__ == '__main__':
    main()

And then elsewhere:

from first_module import main

main(['-f', '/etc/hosts', '-t', 'json'])

Output:

{'group': None, 'file': <_io.TextIOWrapper name='/etc/hosts' mode='r' encoding='UTF-8'>, 'type': 'json'}

edited Jul 28, 2022 at 20:28

marc_s

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answered Jun 24, 2017 at 9:29

Alex Hall

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1 Comment

teichert Over a year ago

and to avoid needing to manually split argument lists: main('-f /etc/hosts -t json'.split()) or if splitting needs to be more sophisticated: import shlex; main(shlex.split('-f /etc/hosts -t json -g "special group name with spaces"')) (shlex is in the standard library.)

Totem · Accepted Answer · 2017-06-24 09:37:29Z

4

There may be a simpler and more pythonic way to do this, but here is one possibility using the subprocess module:

Example:

child_script.py

import argparse

parser = argparse.ArgumentParser()
parser.add_argument("-n", "--name", help="your name")
args = parser.parse_args()

print("hello there {}").format(args.name)

Then another Python script can call that script like so:

calling_script.py:

import subprocess

# using Popen may suit better here depending on how you want to deal
# with the output of the child_script.
subprocess.call(["python", "child_script.py", "-n", "Donny"])

Executing the above script would give the following output:

"hello there Donny"

edited Jun 24, 2017 at 9:37

answered Jun 24, 2017 at 9:31

Totem

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2 Comments

Ryan McGrath Over a year ago

Speaking from experience here, using subprocess to run python instead of importing modules leads to issues down the line. A FileNotFoundException in your subprocess turns into a return code that you have to check and handle with more than you would otherwise have to without subprocess. "except FileNotFoundError: raise" turns into spaghetti with subprocess. This is the tip of the iceberg. For the sake of your future self and coworkers, don't do this.

Tripp Kinetics Over a year ago

Subprocesses cost significant overhead.

be_good_do_good · Accepted Answer · 2017-06-24 09:34:56Z

2

One of the option is to call it as subprocess call like below:

import subprocess
childproc = subprocess.Popen('python childscript.py -file yourjsonfile')
op, oe = childproc.communicate()
print op

answered Jun 24, 2017 at 9:34

be_good_do_good

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1 Comment

Tripp Kinetics Over a year ago

Subprocesses are expensive.

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