Calling a python script with arguments using subprocess

Question

I have a python script which call another python script from another directory. To do that I used subprocess.Popen :

import os
import subprocess

arg_list = [project, profile, reader, file, str(loop)]

where all args are string if not converted implicitely

f = open(project_path + '/log.txt','w')
proc = subprocess.Popen([sys.executable, python_script] + arg_list, stdin=subprocess.PIPE, stdout=f, stderr=f)
streamdata = proc.communicate()[0]
retCode = proc.returncode
f.close()

This part works well, because of the log file I can see errors that occurs on the called script. Here's the python script called:

import time
import csv
import os

class loading(object):

    def __init__(self, project=None, profile=None, reader=None, file=None, loop=None):
        self.project=project
        self.profile=profile
        self.reader=reader
        self.file=file
        self.loop=loop

    def csv_generation(self):       
        f=open(self.file,'a')
        try:
            writer=csv.writer(f)
            if self.loop==True:
                writer.writerow((self.project,self.profile,self.reader))
            else:
                raise('File already completed')
        finally:
            file.close()
def main():
    p = loading(project, profile, reader, file, loop)
    p.csv_generation()

if __name__ == "__main__":
    main()

When I launch my subprocess.Popen, I have an error from the called script which tell me that 'project' is not defined. It looks the Popen method doesn't pass arguments to that script. I think i'm doing something wrong, someone has an idea ?

Why are you using subprocess at all? Why not just import it and call the appropriate functionality directly? — jonrsharpe
– jonrsharpe, Commented Jul 21, 2016 at 14:06
@jonrsharpe because the script called by subprocess is going to be different each time. So dependencies are nerver the same. Moreover that script is not in the same python project as the one which use subprocess. — v_lfr
– v_lfr, Commented Jul 22, 2016 at 9:20
You can import by the name of the script, that's not a problem. And it's not clear what you mean by "not in the same python project", if they're both installed on the same machine that shouldn't be a problem. — jonrsharpe
– jonrsharpe, Commented Jul 22, 2016 at 9:21

cdarke · Accepted Answer · 2016-07-21 14:32:20Z

2

When you pass parameters to a new process they are passed positionally, the names from the parent process do not survive, only the values. You need to add:

import sys
def main():
    if len(sys.argv) == 6:
        project, profile, reader, file, loop = sys.argv[1:]    
    else:
        raise ValueError,("incorrect number of arguments")

    p = loading(project, profile, reader, file, loop)
    p.csv_generation()

We are testing the length of sys.argv before the assignment (the first element is the name of the program).

edited Jul 21, 2016 at 14:32

answered Jul 21, 2016 at 14:26

cdarke

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