Help with the argparse library

Question

I’m trying to use the library argparse to guide the main module (__main__) between two possible executions:

import unittest
import argparse


arg = argparse.ArgumentParser(description='Execution type')
arg.add_argument('--type', action='store', dest='argument', type=int, default=0,
                 required=False, help='Chose the execution type (0=application, 1=unittest)')

options = arg.parse_args()


def main():
    pass


def run_tests():

    from tests import tests_models, tests_dbconnections, tests_dals

    suit = unittest.TestSuite()
    suit.addTest(unittest.makeSuite(tests_models.TestPerson))
    suit.addTest(unittest.makeSuite(tests_models.TestClient))
    suit.addTest(unittest.makeSuite(tests_dbconnections.TestPgSqlConnection))
    suit.addTest(unittest.makeSuite(tests_dals.TestPgSqlDal))

    return suit

if __name__ == '__main__':
    if options.argument:
        unittest.main(defaultTest='run_tests', verbosity=2)
    else:
        main()

But when executing: python3 start.py --type 1

I get an error stating that the argument --type is not recognized: usage: start.py [-h] [-v] [-q] [--locals] [-f] [-c] [-b] [tests [tests ...]] start.py: error: unrecognized arguments: --type

Answer 1

This happens when the unittest takes control, it will interpret the command line options again. --type is a valid argument for the main application, not for the unittest.

You have to separate the command line options from the unittest and the main application. One way to do this is to use argparse.parse_known_args() instead of argparse.parse_args(), see:

(Documentation)

Sometimes a script can only parse some of the command line arguments, passing the remaining arguments to another script or program.

In such cases, the method parse_known_args() can be useful. It works as parse_args() except that it does not produce an error when arguments extras are present. Instead, it returns a tuple of two items containing the namespace populated and the list of remaining arguments.

Code:

import argparse, unittest, sys

parser = argparse.ArgumentParser(description = 'Execution type')
parser.add_argument('--test', action = 'store_true',
                              help = 'Executar o unittest')

options, args = parser.parse_known_args()

def main():
    pass

def run_tests():
    from tests import tests_models, tests_dbconnections, tests_dals

    suit = unittest.TestSuite()
    suit.addTest(unittest.makeSuite(tests_models.TestPerson))
    suit.addTest(unittest.makeSuite(tests_models.TestClient))
    suit.addTest(unittest.makeSuite(tests_dbconnections.TestPgSqlConnection))
    suit.addTest(unittest.makeSuite(tests_dals.TestPgSqlDal))

    return suit

if __name__ == '__main__':
    if options.test:
        sys.argv[1:] = args
        unittest.main(defaultTest = 'run_tests', verbosity = 2)
    else:
        main()

To call the unittest do:

python3 nomedoScript.py --test

To run the main application call the script unencumbered:

python3 nomedoScript.py