[Tutor] lockfiles and timestamps and nested if's!

[Roeland Rengelink]

kromag@nsacom.net wrote:
> 
> I am attempting a silly thing. I wish to make a script that will:
> 


> 1. Check for the existence of a lockfile.
> 2. Check the age of the lockfile.
> 
> Then either:
> Delete the lockfile if it is too old and continue,
> or
> exit gracefully.
> 
> I have managed to get myself into a dither here. The script for some reason
> always writes a new lock file and updates the timestamp. Can someone clue me
> in? My brain is full.
> 
> import glob
> import time
> import string
> import os
> import socket
> 
> now=time.time()
> mybox=socket.gethostname()+'.txt'
> whoa=glob.glob('\tmp\*')

print whoa here, to see if the next test makes sense.
use os.listdir in stead of glob

> if whoa==['\tmp\'+mybox]:
>         lockfile=open('\tmp\'+mybox, 'r')
>         timestamp=lockfile.readline()
>         print timestamp
>         lockfile.close()
>         if timestamp > time.time()-10:

You are comparing the string timestamp with the float time.time
Are you sure you want to delete lockfiles older than 10 seconds?

>                 print 'old lockfile ok',
>         else:
>                 os.remove('\tmp\'+mybox)
> 

Are you sure the lockfile shouldn't be recreated now?

> else:

The easiest way to end up here is if there's more than one file in \tmp\

>         lockfile=open('\tmp\'+mybox, 'w')
>         lockfile.write(`now`)
>         print 'new lockfile'
>         print 'and contiue with the rest of this balderdash!
> 
> _______________________________________________
> Tutor maillist  -  Tutor@python.org
> http://mail.python.org/mailman/listinfo/tutor

OK here's what I understand you want to do:

import time, os, socket, 
import string

now = time.time()
lockfilename = socket.gethostname()+'.txt'

if lockfilename in os.listdir('/tmp'):
    contents = open('/tmp/'+lockfilename,'r').readline()
    timestamp = float(string.strip(contents))
    # use contents.strip() in Python2.0

    if timestamp < now-10:
	# the timestamp is old, we have to rewrite the file
	# I'm not sure if this is actually what you want to do here
        f = open('/tmp/'+lockfilename,'w')
        f.write(str(now)+'\n')
else:
    # the file doesn't exist at all, we have to write it
    f = open('/tmp/'+lockfilename,'w')
    f.write(str(now)+'\n')
   
Hmm. two code blocks doing the same thing is ugly

Maybe
- put lockfile creation and lockfile checking in functions ?
- use exceptions ?

Ah, this works anyway.

Hope this helps,

Roeland

-- 
r.b.rigilink@chello.nl

"Half of what I say is nonsense. Unfortunately I don't know which half"