File Polling (Rereading)

[John Taylor]

Daniel Mueller <da_mueller at gmx.net> wrote in message news:<cl85jb$2rfa$1 at news.imp.ch>...
> Hello Fellow Python Programmers,
> 
> I have the following problem:
> 
> i want to read the content of a file every 10 seconds. now what is the 
> best funktion to do that? to open the file, read it and close it 
> consumes a lot of CPU time. is there a better solution?
> 
> Greetings Daniel

Daniel,

I have written a python program that does this.  It does not use a lot
of CPU cycles.  You need to change the SLEEP variable from 0.50 to 10.
 I have used it on Windows and on Linux.  Here it is...

-John

#!/usr/bin/env python
"""
tail.py
John Taylor, Oct 19 2004
Adapted from:
http://groups.google.com/groups?hl=en&lr=&selm=mailman.1028401086.15956.python-list%40python.org
"""

import sys,os,time,stat
SLEEP = 0.50

if len(sys.argv) != 2:
	print
	print "tail.py [ filename ]"
	print
	sys.exit(1)

FILENAME = sys.argv[1]

try:
	fd = os.open(FILENAME,os.O_RDONLY) # on Linux, may want |O_LARGEFILE
except OSError, e:
	print e
	sys.exit(1)

info = os.fstat( fd )
lastsize = info[stat.ST_SIZE]
os.lseek( fd, lastsize, 2 )

try:
	while True:
		info = os.fstat( fd )
		size = info[stat.ST_SIZE]
		if size > lastsize:
			os.lseek(fd, lastsize, 0)
			data = os.read(fd, size - lastsize)
			print data,
			lastsize=size
		time.sleep( SLEEP )
except KeyboardInterrupt:
	pass

# end of program