Newbie: executing a system command from my Python app

[James Stroud]

Dan M wrote:
> I'm writing a Python replacement for a particularly ugly shell script. we
> are running mimedefang on our mail server, moving spam and virus messages
> to a quarantine directory. This little python script successfully chdir's
> to the quarantine directory, identifies all of the quarantine
> subdirectories for yesterday's messages, and stuffs them into a tar file
> in an archive directory. I then want to delete for successfully tarred
> files and the subdirs they live in.
> 
> By way of further explanation, quarantined messages get broken into files
> named ENTIRE_MESSAGE, HEADERS, RECIPIENTS, SENDER, and SENDMAIL-QID, and
> get stored in subdirectories named qdir-YYYY-MM-DD-hh.mm.ss-nnn, where
> Y-M-D is the date received, hms is time received, and nnn is to allow for
> up to 10 messages to quarantined any given second.
> 
> I know I can do this by descending into the directories I've identified
> and unlink()ing each of the files, but I'd like to take a shortcut like:
> "retval = os.system('rm -rf /var/spool/MD-Quarantine/qdir-%s*' %
> (dateYest))" and indeed code written that executes without any errors.
> Unfortunately it also leaves a bunch of qdir-2005-12-11-* files sitting
> around when I run it on 12-11.

Few points points:

1. Generally: I would try to minimize system calls. They make your code less
    portable.
2. Look into the "shutil" module for recursive deletion.
3. Use os.path to construct paths. Try to avoid, for example,
    "c:\blah\blah" on dos, '/blah/blah' on unix, etc.
4. If you only have one argument, you don't need a tuple for string formatting.
5. "(dateYest)" is not a tuple anyway--the parentheses are superfluous
6. Single item tuples can be created with "(anitem,)" (notice the comma).

James