Posts Tagged ‘Python’

Using subprocess for popen

June 16, 2010 1 comment

While trying to use a Python script today I came across this:

/usr/local/lib/python2.6/site-packages/londiste/ DeprecationWarning: os.popen4 is
deprecated.  Use the subprocess module.
s_in , s_out = os.popen4("sort –version")

The troubling code:

s_in, s_out = os.popen4("sort --version")

Now this is because with Python 2.6 and above ‘popen4’ is something that is a depreciated feature, which means it will be better to change it to use ‘subprocess’ in order to get rid of the warning message.

A replacement to that is by using ‘subprocess’ as…

p = subprocess.Popen("sort --version", shell=True, stdin=subprocess.PIPE,
stdout=subprocess.PIPE, stderr=subprocess.STDOUT, close_fds=True)
(s_in, s_out) = (p.stdin, p.stdout)

For using subprocess, you will have to add this as well:

import subprocess

Using subprocess instead of popen does the same thing and gets rid of the annoying warning.

Shoaib Mir

import subprocess
Categories: Python Tags: , ,

Application lock file implementation

January 23, 2010 Leave a comment

Its always a good practice to put a check in the code to see if another instance of the same app is running.

This is helpful in case you have a cron job that is called every hour and single execution of an app can take more then a hour, in this case if we dont have a check in place then that means we can have more then one instance of the same at one time.

Recently I had to add the same kind of check for one of my Python scripts, sharing that if it might help someone trying to do the same:

if os.access(os.path.expanduser("~/.application.lock"), os.F_OK):
       lck_fl = open(os.path.expanduser("~/.application.lock"), "r")
       oldpid = lck_fl.readline()
       if os.path.exists("/proc/%s" % oldpid):
           print "lck_fl exist! process is already running"
           print "Process is already running as pid %s," % oldpid
           print "lck_fl exists but no PID found as current process"
           print "Removing lck_fl of application process: %s" % oldpid
lck_fl = open(os.path.expanduser("~/.application.lock"), "w")
lck_fl.write("%s" % os.getpid())

Shoaib Mir

Categories: Python Tags: ,

PID lock file in python

December 14, 2009 2 comments

I have a python script which when running on large disks can (rarely) run on for like more then a hour, and then I have got this cron setup which runs this script and the cron is set to run every hour. This means I can have several instances of the same Python script at one time. In order to get rid of that kind of scenario I did basic style of pid lock file implementation today:

#This is to check if there is already a lock file existing#
if os.access(os.path.expanduser("~/.lockfile.vestibular.lock"), os.F_OK):
        #if the lockfile is already there then check the PID number 
        #in the lock file
        pidfile = open(os.path.expanduser("~/.lockfile.vestibular.lock"), "r")
        old_pd = pidfile.readline()
        # Now we check the PID from lock file matches to the current
        # process PID
        if os.path.exists("/proc/%s" % old_pd):
                print "You already have an instance of the program running"
                print "It is running as process %s," % old_pd
                print "File is there but the program is not running"
                print "Removing lock file for the: %s as it can be there
                because of the program last time it was run" % oldpid

#This is part of code where we put a PID file in the lock file
pidfile = open(os.path.expanduser("~/.lockfile.vestibular.lock"), "w")
pidfile.write("%s" % os.getpid())

Hope this can help someone doing the same.

Shoaib Mir

Categories: Python Tags: , ,

Option parser in Python

November 18, 2009 Leave a comment

I have just started playing around with Python like a few weeks back and having lots of fun scripting in it. Today at work got to know of a very nice feature with Python which lets you easily configure the options taken from command line, which is called option parser.

Firstly, you need to include the library with ‘import’:

from optparse import OptionParser

Now you can use it like this:

usage = "usage: %prog -H hostname -p port -d diskpath -t threshold"
parser = OptionParser(usage=usage, version="%prog 1.0")
parser.add_option("-H", "--host", action="store", type="string", dest="hostname",
help="input host name for database server")
parser.add_option("-d", "--disk", action="store",
type="string", dest="diskpath", help="input disk path")
parser.add_option("-p", "--port", action="store", type="string",
dest="dbport", help="input port for database server")
parser.add_option("-t", "--thresh", action="store", type="int",
dest="thresh", help="input threshold for disk size ")

Where every add_option means adding a new argument on command line to check for and the best thing is you just put in the help section with the add_option function call and it automagically builds the full help section for the program to be use with “-h”, so that means you cant have an option with “-h” as that clashes with the default help option for option parser, and that was the reason I had to go with “-H” for hostname 🙂

In order to get the values into variables just simply use:

(options, args) = parser.parse_args()
if options.hostname:
if options.diskpath:
if options.dbport:
if options.thresh:

Now when you run the program with “-h” option you get the following:

shoaib@shoaib-desktop:~/Desktop/Scripts$ ./mgmnt -h
Usage: mgmnt -H hostname -p port -d diskpath -t threshold
--version             show program's version number and exit
-h, --help            show this help message and exit
input host name for database server
input disk path
-p DBPORT, --port=DBPORT
input port for database server
-t THRESH, --thresh=THRESH
input threshold for disk size

Shoaib Mir

Categories: Python Tags: ,