Call a Python function in a file with command-line argument

Question

I'm trying to pass arguments from Node.js to Python with child_process spawn. I also want to invoke the specific Python function with one of the argument that I specified in the Node.js array.

test.js

'use strict';

const path = require('path');
const spawn = require('child_process').spawn;

const exec = (file, fnCall, argv1, argv2) => {
  const py = spawn('python', [path.join(__dirname, file), fnCall, argv1, argv2]);
  py.stdout.on('data', (chunk) => {
    const textChunk = chunk.toString('utf8'); // buffer to string
    const array = textChunk.split(', ');
    console.log(array);
  });
};
exec('lib/test.py', 'test', 'argument1', 'argument2'.length - 2);  // => [ 'argument1', '7' ]
exec('lib/test.py', 'test', 'arg3', 'arg4'.length - 2);  // => [ 'arg3', '2' ]

The second argument here is test, which should call the test() Python function.

lib/test.py:

import sys

def test():
    first_arg = sys.argv[2]
    second_arg = sys.argv[3]
    data = first_arg + ", " + second_arg
    print(data, end="")

sys.stdout.flush()

If I try to run this Python file without any Node.js from the command line, the execution looks like this:

$ python lib/test.py test arg3 2

Where test, arg3, and 2 are just command-line arguments, but test should call the test() function, which will use the arg3, 2 arguments for print().

Avantol13 · Accepted Answer · 2016-08-31 19:01:46Z

4

I'd recommend using argparse to parse the command line arguments. Then you can use eval to get the actual function from the input.

import argparse

def main():
    # Parse arguments from command line
    parser = argparse.ArgumentParser()

    # Set up required arguments this script
    parser.add_argument('function', type=str, help='function to call')
    parser.add_argument('first_arg', type=str, help='first argument')
    parser.add_argument('second_arg', type=str, help='second argument')

    # Parse the given arguments
    args = parser.parse_args()

    # Get the function based on the command line argument and 
    # call it with the other two command line arguments as 
    # function arguments
    eval(args.function)(args.first_arg, args.second_arg)

def test(first_arg, second_arg):
    print(first_arg)
    print(second_arg)

if __name__ == '__main__':
    main()

answered Aug 31, 2016 at 19:01

Avantol13

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3 Comments

Lanti Over a year ago

Thank You! Works perfectly!

Avantol13 Over a year ago

@Lanti No problem, glad to help

Tengerye Over a year ago

What if the number of parameters required for each function is different?

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