Running external program using pipes and passing arguments in python

Question

I tried that, but when I try to print these arguments it returns no values. I submit my code below:

script1 that runs external python program (script2)

#(...)
proc = subprocess.Popen(['export PYTHONPATH=~/:$PYTHONPATH;' +
    'export environment=/path/to/environment/;' +
    'python /path/to/my/program/myProgram.py',
    '%(date)s' %{'date':date}, '%(time)s' %{'time':time}],
    stdin=PIPE, stdout=PIPE, stderr=PIPE, shell=True)
#(...)

script2 that is being run by the script1

#(...)
print sys.argv[0] #prints the name of the command
print sys.argv[1] #it suppose to print the value of the first argument, but it doesn't
print sys.argv[2] #it suppose to print the value of the second argument, but it doesn't
#(...)

have you tried using shlex.split ?

BrainStorm
– BrainStorm

2011-08-09 21:47:05 +00:00
Commented Aug 9, 2011 at 21:47 — BrainStorm
– BrainStorm, Commented Aug 9, 2011 at 21:47
no, not really, would that help?

Python_beginner
– Python_beginner

2011-08-09 22:11:55 +00:00
Commented Aug 9, 2011 at 22:11 — Python_beginner
– Python_beginner, Commented Aug 9, 2011 at 22:11

agf · Accepted Answer · 2011-08-09 22:31:41Z

1

Try this version of script 1:

proc = subprocess.Popen('python /path/to/my/program/myProgram.py %s %s' % (date, time),
                        stdin=PIPE, stdout=PIPE, stderr=PIPE, shell=True,  
                        env = {'PYTHONPATH': '~/:$PYTHONPATH',
                               'environment': '/path/to/environment/'})

It should make it easier to find your problem if it doesn't work; but I think it will.

edited Aug 9, 2011 at 22:31

answered Aug 9, 2011 at 21:47

agf

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3 Comments

Python_beginner Over a year ago

unfortunately it didn't work, in fact it wouldn't even print the output of script2

agf Over a year ago

Did you try it after my edit? And did you try it WITHOUT the =PIPE arguments?

Python_beginner Over a year ago

I just tried without =PIPE arguments, but it throws error, as it cannot import library, so it probably didn't set the envelope correctly

Dunes · Accepted Answer · 2011-08-09 21:48:37Z

1

Docs say that when specifying shell=True any additional args are treated as args to the shell, not to the command. To make it work, just set shell to False. I don't see why you need it to be True.

edit: I see you want to use shell to set environment variables. Use the env argument to set the environment variables instead.

answered Aug 9, 2011 at 21:48

Dunes

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3 Comments

senderle Over a year ago

The other two answers address important issues, but this is the main problem.

Python_beginner Over a year ago

I need shell to be true, as I need to export libraries first

Dunes Over a year ago

Like I said. Use env argument to set the environment instead. If you need to copy any environment variables from your current environment then copy environ in the os module.

unutbu · Accepted Answer · 2011-08-09 22:19:25Z

1

Use Popen's env parameter to pass environment variables:
Don't use shell=True unless you have to. It can be a security risk (see Warning).

test.py:

import subprocess
import shlex
import datetime as dt
now=dt.datetime.now()
date=now.date()
time=now.strftime('%X')

proc = subprocess.Popen(shlex.split(
    'python /tmp/test2.py %(date)s %(time)s'%{'date':date,
                                         'time':time}),
                        stdout=subprocess.PIPE,
                        stderr=subprocess.PIPE,
                        env={'PYTHONPATH':'~/:$PYTHONPATH',
                             'environment':'/path/to/environment/'})

out,err=proc.communicate()
print(out)
print(err)

test2.py:

import sys
import os

print(os.environ['PYTHONPATH'])
print(os.environ['environment'])
for i in range(3):
    print(sys.argv[i])

yields

~/:$PYTHONPATH
/path/to/environment/
/tmp/test2.py
2011-08-09
17:50:04

edited Aug 9, 2011 at 22:19

answered Aug 9, 2011 at 21:51

unutbu

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1 Comment

agf Over a year ago

If print sys.argv[0] is working, then the pipes aren't his problem. Good call on the env parameter.

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