Run a Python script from another Python script, passing in arguments

The Question :

352 people think this question is useful

I want to run a Python script from another Python script. I want to pass variables like I would using the command line.

For example, I would run my first script that would iterate through a list of values (0,1,2,3) and pass those to the 2nd script script2.py 0 then script2.py 1, etc.

I found Stack Overflow question 1186789 which is a similar question, but ars’s answer calls a function, where as I want to run the whole script, not just a function, and balpha’s answer calls the script but with no arguments. I changed this to something like the below as a test:

execfile("script2.py 1")

But it is not accepting variables properly. When I print out the sys.argv in script2.py it is the original command call to first script “[‘C:\script1.py’].

I don’t really want to change the original script (i.e. script2.py in my example) since I don’t own it.

I figure there must be a way to do this; I am just confused how you do it.

The Question Comments :
  • If os.system isn’t powerful enough for you, there’s the subprocess module.
  • The question is if you know the name of the script (then import it) or if you do not know the name of the script at programming time (then use subprocess.call). In the second case this question also would not be a duplicate. Because the question doesn’t make it clear, it’s also not really a good one.
  • @Trilarion: wrong. You can import a python module even if its name is generated at runtime.
  • @Trilarion: why should it be covered at all? The names are fixed in both questions. Anyway, the statement “if you do not know the name of the script at programming time (then use subprocess.call).” is wrong regardless. If you have a new question; ask.
  • @Oli4 “definitely” is a strong word. Care to elaborate? I see subprocess.call() solution that accepts passing multiple command line arguments. I see import being mentioned for cases where main() function is defined (it won’t help OP but it is the right way for many other people with a similar problem). I see execfile() for Python 2 that uses whatever you put into sys.argv (admittedly that last bit is not mentioned explicitly) — this option should be ignored by beginners. There is even an explicit os.system() answer with multiple arguments (the answer that is accepted here).

The Answer 1

348 people think this answer is useful

Try using os.system:

os.system("script2.py 1")

execfile is different because it is designed to run a sequence of Python statements in the current execution context. That’s why sys.argv didn’t change for you.

The Answer 2

116 people think this answer is useful

This is inherently the wrong thing to do. If you are running a Python script from another Python script, you should communicate through Python instead of through the OS:

import script1

In an ideal world, you will be able to call a function inside script1 directly:

for i in range(whatever):
    script1.some_function(i)

If necessary, you can hack sys.argv. There’s a neat way of doing this using a context manager to ensure that you don’t make any permanent changes.

import contextlib
@contextlib.contextmanager
def redirect_argv(num):
    sys._argv = sys.argv[:]
    sys.argv=[str(num)]
    yield
    sys.argv = sys._argv

with redirect_argv(1):
    print(sys.argv)

I think this is preferable to passing all your data to the OS and back; that’s just silly.

The Answer 3

104 people think this answer is useful

Ideally, the Python script you want to run will be set up with code like this near the end:

def main(arg1, arg2, etc):
    # do whatever the script does


if __name__ == "__main__":
    main(sys.argv[1], sys.argv[2], sys.argv[3])

In other words, if the module is called from the command line, it parses the command line options and then calls another function, main(), to do the actual work. (The actual arguments will vary, and the parsing may be more involved.)

If you want to call such a script from another Python script, however, you can simply import it and call modulename.main() directly, rather than going through the operating system.

os.system will work, but it is the roundabout (read “slow”) way to do it, as you are starting a whole new Python interpreter process each time for no raisin.

The Answer 4

46 people think this answer is useful

I think the good practice may be something like this;

import subprocess
cmd = 'python script.py'

p = subprocess.Popen(cmd, stdout=subprocess.PIPE, shell=True)
out, err = p.communicate() 
result = out.split('\n')
for lin in result:
    if not lin.startswith('#'):
        print(lin)

according to documentation The subprocess module allows you to spawn new processes, connect to their input/output/error pipes, and obtain their return codes. This module intends to replace several older modules and functions:

os.system
os.spawn*
os.popen*
popen2.*
commands.*

Use communicate() rather than .stdin.write, .stdout.read or .stderr.read to avoid deadlocks due to any of the other OS pipe buffers filling up and blocking the child process. Read Here

The Answer 5

45 people think this answer is useful

SubProcess module:
http://docs.python.org/dev/library/subprocess.html#using-the-subprocess-module

import subprocess
subprocess.Popen("script2.py 1", shell=True)

With this, you can also redirect stdin, stdout, and stderr.

The Answer 6

31 people think this answer is useful
import subprocess
subprocess.call(" python script2.py 1", shell=True)

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