Use argparse to send arguments to function within Python script

Question

I am in the bit of a weird situation where I need a Python function to run from within a script, with the script then called from my main code.

I wanted to use the subprocess module, and know how to use it to pass arguments to a pure script, but the thing is, I need to pass the arguments to the nested Python function within, most of which are optional and have default values.

I thought arparse would help me do this somehow.

Here is an example of what I am trying:

## Some Argparse, which will hopefully help
import argparse

parser = argparse.ArgumentParser()

## All arguments, with only "follow" being required
parser.add_argument('file_name', help='Name of resulting csv file')
parser.add_argument('sub_name', help='Sub-name of resulting csv file')
parser.add_argument('follow', help='Account(s) to follow', required=True)
parser.add_argument('locations', help='Locations')
parser.add_argument('languages', help='Languages')
parser.add_argument('time_limit', help='How long to keep stream open')

args = parser.parse_args()


## Actual Function
def twitter_stream_listener(file_name=None,
                            sub_name='stream_',
                            auth = api.auth,
                            filter_track=None,
                            follow=None,
                            locations=None,
                            languages=None,
                            time_limit=20):
   ... function code ...
   ... more function code ...
   ...
   ...
   ## End of script

`argparse` just takes the strings in `sys.argv` (or some other list you pass explicitly to `parse_args`) and gives you the object `args`. What you do with `args` is up to you. You might treat it as a global variable, or pass it as an additional argument to `twitter_stream_listener`, or just pass the individual attributes as arguments where needed. — chepner, Feb 15 '19 at 15:24
Are you sure you need to use `subprocess` to start program A and execute function `A.twitter_stream_listener()` inside it? A much simpler approach would be to have your code `import A` and call `A.twitter_stream_listener()` directly. — BoarGules, Feb 15 '19 at 15:47
aaaakshat, I am not receiving any errors, just am not sure how to structure my code to send my parsed arguments to my function. BoarGules, I wanted to do that at first, but my function in question was written by someone else, and I do not know how to refactor it to allow me to close said function midway (without affecting any other processes in the rest of the kernel), so I am trying to give it its own sub-process, which seems easier to close on-the-fly. — Coolio2654, Feb 15 '19 at 16:29

score 5 · Accepted Answer · answered Feb 15 '19 at 16:15

If you are passing arguments to functions all you need to do is feed them into the function when you're executing them:

import argparse

parser = argparse.ArgumentParser()
parser.add_argument("-o", "--output_file_name", help="Name of resulting csv file")
parser.add_argument("-s", "--sub_name", default="stream_", help="Sub-name of resulting csv file")
parser.add_argument("-f", "--follow", help="Account(s) to follow", required=True)
parser.add_argument("-loc", "--locations", default=None, help="Locations")
parser.add_argument("-lan", "--languages", default=None, help="Languages")
parser.add_argument("-t", "--time_limit", default=20, help="How long to keep stream open")

options = parser.parse_args()

# then just pass in the arguments when you run the function
twitter_stream_listener(file_name=options.output_file_name,
                        sub_name=options.sub_name, 
                        auth=api.auth,
                        filter_track=None,
                        follow=options.follow,
                        locations=options.locations,
                        languages=options.languages,
                        time_limit=options.time_limit)


# or, pass the arguments into the functions when defining your function
def twitter_stream_listener_with_args(file_name=options.output_file_name,
                                      sub_name=options.sub_name, 
                                      auth=api.auth,
                                      filter_track=None,
                                      follow=options.follow,
                                      locations=options.locations,
                                      languages=options.languages,
                                      time_limit=options.time_limit):
    # does something
    pass

# then run with default parameters
twitter_stream_listener_with_args()

score 1 · Answer 2 · answered Feb 15 '19 at 15:49

You can specify defaults in the argparse section (if that is what you are trying to achieve):

#!/usr/bin/python
import argparse
parser = argparse.ArgumentParser()

parser.add_argument('--argument', default = 'something', type = str, help = 'not helpful')
parser.add_argument('--arg2', default = None, type = str, help = 'not helpful')


args = parser.parse_args()

def foo(arg , arg2 ):
    print(arg)
    if not arg2 is  None:
        print(arg2)

foo(args.argument, args.arg2)

Then calling:

$ ./test.py
something

$ ./test.py --argument='somethingelse'
somethingelse

$ ./test.py --arg2=123
something
123

$ ./test.py --arg2='ipsum' --argument='lorem'
lorem
ipsum

Is this helpful?

machnic · Answer 3 · 2019-02-15T16:10:36.513

You can do it like that:

import argparse

## Actual Function
def twitter_stream_listener(file_name=None,
                            sub_name='stream_',
                            auth=api.auth,
                            filter_track=None,
                            follow=None,
                            locations=None,
                            languages=None,
                            time_limit=20):

    # Your content here


if __name__ == '__main__':
    parser = argparse.ArgumentParser()

    ## All arguments, with only "follow" being required
    parser.add_argument('follow', help='Account(s) to follow')
    parser.add_argument('--file_name', help='Name of resulting csv file')
    parser.add_argument('--sub_name', help='Sub-name of resulting csv file')
    parser.add_argument('--locations', help='Locations')
    parser.add_argument('--languages', help='Languages')
    parser.add_argument('--time_limit', help='How long to keep stream open')

    args = parser.parse_args()

    twitter_stream_listener(file_name=args.file_name, sub_name=args.sub_name, follow=args.follow,
                            locations=args.locations, languages=args.languages, time_limit=args.time_limit)

follow will be the only required argument and the rest optional. Optional ones have to be provided with -- at the beginning. You can easily use the module with subprocess if you need it.

Example call using command line:

python -m your_module_name follow_val --file_name sth1 --locations sth2

Since I am still a bit of a newbie to Python scripting, what does the `if __name__ == '__main__':` section achieve here? Couldn't I just use your example without that? — Coolio2654, Feb 15 '19 at 16:35
This stackoverflow answer will explain it much better than I could possibly do in a single comment: https://stackoverflow.com/a/419185/3603682 — machnic, Feb 15 '19 at 16:38

Use argparse to send arguments to function within Python script

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