Running Bash commands in Python

Question

On my local machine I run a python script which contains this line

bashCommand = "cwm --rdf test.rdf --ntriples > test.nt"
os.system(bashCommand)

This works fine.

Then I run the same code on a server and I get the following error message

'import site' failed; use -v for traceback
Traceback (most recent call last):
File "/usr/bin/cwm", line 48, in <module>
from swap import  diag
ImportError: No module named swap

So what I did then is I inserted a "print bashCommand" which prints me then the command in the terminal before it runs it with os.system().

Of course I get again the error (caused by os.system(bashCommand)) but before that error it prints the command in the terminal. Then I just copied that output and did a copy paste into the terminal and hit enter and it works...

Does anyone have a clue what's going on :(?

Answer 1

According to the error you are missing a package named swap on the server. This /usr/bin/cwm requires it. If you're on Ubuntu/Debian, install python-swap using aptitude.

Answer 2

The pythonic way of doing this is using subprocess.Popen

subprocess.Popen takes a list where the first element is the command to be run followed by any command line arguments.

As an example:

import subprocess

args = ['echo', 'Hello!']
subprocess.Popen(args) // same as running `echo Hello!` on cmd line

args2 = ['echo', '-v', '"Hello Again"']
subprocess.Popen(args2) // same as running 'echo -v "Hello Again!"` on cmd line

Answer 3

Also you can use 'os.popen'. Example:

import os

command = os.popen('ls -al')
print(command.read())
print(command.close())

Output:

total 16
drwxr-xr-x 2 root root 4096 ago 13 21:53 .
drwxr-xr-x 4 root root 4096 ago 13 01:50 ..
-rw-r--r-- 1 root root 1278 ago 13 21:12 bot.py
-rw-r--r-- 1 root root   77 ago 13 21:53 test.py

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