How to call input parameters into another python file using argparse?

Question

I have the following files in a python pipeline

#in_para.py

nx = 31
c = 1

#solver.py
import numpy
import os   

def simple(output):
    ny = nx + 5
    c_2 = c + 2
    with open(os.path.join(output, 'Output.txt'), 'w') as f:
         print("Hello stackoverflow!", file=f)
         print("I have a question.", file=f)
        
if __name__=='__main__':
    simple()

#main.py 

import os
import numpy
import argparse

def main():
    parser = argparse.ArgumentParser() 
    parser.add_argument('-C','--Chk',type=str, help='Choose arg')
    parser.add_argument('-O','--output',type=str, default="./Output", help=' Provide the output Directory')

    args = vars(parser.parse_args())
 
    output = args['output']
    if not os.path.exists(output):
        os.makedirs(output)

    if args['Chk'] == 'compo1':
        simple(output)
    
if __name__=='__main__':
    main()

I would like to call the input file in_para.py through command line argument such that

python3 main.py -I in_para -C compo1 -O Ouput_dir

gives me the desired output:

this is a simple test 36
this is a simple test2 3

I know if I do from in_para import * it will solve the problem (in a different manner), but I would like to call the input parameters from the command line as a positional argument and pass it on to solver.py. I haven't been able to find an example in the documentation similar to above task. Besides, the above is just an example, in_para.py and solver.py has several input parameters and several lines of code, so I dont want the user of main.py to go into either file and modify it.

Try docs.python.org/3/library/argparse.html#fromfile-prefix-chars — Carlos Horn
– Carlos Horn, Commented Jun 27, 2022 at 8:19
@CarlosHorn its not about having large set of input parameters, I would like to import it via an input file using argparse in main.py and pass it on to the solver.py — newstudent
– newstudent, Commented Jun 27, 2022 at 8:24
You could also make your function in solver.py explicit and pass the input arguments like def simple(nx, c) this will allow you to implement any logic on providing the input, e.g. parse a yaml file which was given as command line argument. — Carlos Horn
– Carlos Horn, Commented Jun 27, 2022 at 8:29
Or is it important that the input file is a python file, e.g. because some parameters are computed there? — Carlos Horn
– Carlos Horn, Commented Jun 27, 2022 at 8:34

Carlos Horn · Accepted Answer · 2022-06-28 08:49:38Z

1

Change the implementation in solver.py

def simple(nx, c, output):  # provide parameters as function arguments
    ny = nx + 5
    c_2 = c + 2
    print("this is a simple test", ny)
    print("this is a simple test2", c_2)
    with open(os.path.join(output, 'Output.txt'), 'w') as f:
        print("Hello stackoverflow!", file=f)
        print("I have a question.", file=f)

In the main parse the parameters file

...  # other imports
import json

def main():
    parser = argparse.ArgumentParser() 
    parser.add_argument('-C','--Chk', type=str, help='Choose arg')
    parser.add_argument('-I','--input', type=argparse.FileType("r"), help='Input parameters')
    parser.add_argument('-O','--output', type=str, help='output dir')
    args = parser.parse_args()
    output = args.output
    # implement any way of parsing the input file, e.g. a json file
    params = json.load(args.input)
    
    ...  # do something else with the arguments
 
    if args.Chk == 'compo1':
        simple(output=output, **params)

...  # further code lines

Your inputs file would look like

{"nx": 31, "c": 1}

Comment on edit:

Either you use args = vars(parser.parse_args()) which results in a dictionary or you just use the args = parser.parse_args() to select arguments by attribute. In your original post you used the first approach which I adopted in the first answer. However, I would prefer not using vars. Note, that the code snippet to create the directory does not add value to the actual question of the post, so I removed it to avoid any distraction and added some placeholder instead.

edited Jun 28, 2022 at 8:49

answered Jun 27, 2022 at 8:49

Carlos Horn

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9 Comments

Carlos Horn Over a year ago

Note, this implementation uses a json file, but as @BoarGules suggested, you could also use an ini file parsed with configparser or even write your own parser (not recommended if json or ini files can do the job) another popular format is yaml, which is more focused on human readable than json, but it is not part of the standard python library.

newstudent Over a year ago

May I know why you have modified the solver.py ?

Carlos Horn Over a year ago

Because the function simple should receive the parameters as argument instead of getting them from the global namespace.

newstudent Over a year ago

actually there shouldnt be nx in solver.py in the first place. that is a typo

Carlos Horn Over a year ago

In any case, the point is to provide parameters as input arguments, so you have more flexibility on where you get them from. I would not recommend to work with globals here.

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