cannot pass arguments to python script when invoke from subprocess

Question

I have searched SO but couldn't find an asnwer. I want to invoke a python script(child script) from another python script(main script). I cannot pass arguments from parent to child? I am expecting "subprocess launched: id1-id2" from the console. But what I am getting is "subprocess launched:test-default". The subprocess is using the default parameters instead of receiving parameters from the parent script.

# parent
import subprocess
subprocess.call(['python', 'child.py', 'id1', 'id2'])

# script name: child.py
def child(id, id2):
    print ('subprocess launched: {}-{}'.format(str(id), id2))

if __name__ == '__main__':
    main(id='test', id2='default')

Furthermore you can, but these parameters are in sys.args. — willeM_ Van Onsem
– willeM_ Van Onsem, Commented Aug 4, 2019 at 20:11
sorry didn't get what you are saying. I want a subprocess instead of call main directly. That way my parent scrip can keep going instead of waiting for the child to complete.@WillemVanOnsem — Lisa
– Lisa, Commented Aug 4, 2019 at 20:13
every script get arguments from command line in sys.args but your child.py doesn't use sys.argv — furas
– furas, Commented Aug 4, 2019 at 20:15
@Lisa, ...if that's all you're trying to do, there are cheaper/more efficient ways to fork() a copy of your current interpreter with startup-time initialization already done; when you use subprocess to start a whole new interpreter, it pays what would otherwise be one-time startup costs a second time. See the multiprocessing module for an example. And of course, there's also threading (though whether that's appropriate depends on implementation details). — Charles Duffy
– Charles Duffy, Commented Aug 4, 2019 at 20:59

willeM_ Van Onsem · Accepted Answer · 2019-08-04 20:18:14Z

2

The parameters that you pass to a Python process are stored in sys.argv [Python-doc]. This is a list of parameters, that works a bit similar to $@ in bash [bash-man] for example.

Note that argv[0] is not the first parameter, but the name of the Python script you run, as is specified by the documentation:

argv[0] is the script name (it is operating system dependent whether this is a full pathname or not).

The remaining parameters are the parameters passed to the script.

You can thus rewrite your child.py to:

# script name: child.py
from sys import argv

def child(id, id2):
    print ('subprocess launched: {}-{}'.format(str(id), id2))

if __name__ == '__main__':
    child(id=argv[1], id2=argv[2])

edited Aug 4, 2019 at 20:18

answered Aug 4, 2019 at 20:15

willeM_ Van Onsem

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1 Comment

Chris_Rands Over a year ago

;) i think you mean: from sys import argv

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