Question

I was wondering whether or not it is considered a good style to call bash commands within a Python script using os.system(). I was also wondering whether or not it is safe to do so as well.

I know how to implement some of the functionality I need in Bash and in Python, but it is much simpler and more intuitive to implement it in Bash. However, I feel like it is very hackish to write os.system(“bash code”).

Specifically, I want to move all files that end with a certain extension to a directory.

In bash: *mv .ext /path/to/destination
In Python (Pseudocode):
for file in directory:
if file.endswith(“ext”):
move file to destination

In this case, what should I do?

Answer 1

First of all, your example uses mv, which is a program in coreutils, not bash.

Using os.system() calls to external programs is considered poor style because:

• You are creating platform-specific dependencies
• You are creating version-specific dependencies (Yes, even coreutils change sometimes!)
• You need to check for the existence of external commands (and that they are in $PATH, and executable by the user etc.)
• You have to wrap the commands with error checking using their return code. It is much nicer to use in-language error-codes or exceptions. (os.system() does not let you parse stdout/stderr)
• You have to deal with quoting variables with spaces yourself (or escaping them)
• Python has already done the work for you by supplying the libraries!

Look up glob, for shell-like pattern matching (globbing), and shutil, as others have already mentioned. Otherwise, everything you need is already in the standard libraries.

import glob
import shutil

for extfile in glob.glob('*.ext'):
    shutil.move(extfile,dest)  

In addition, os.system() should not be used – take a look at the subprocess module instead.