[Tutor] piping continuous output

[Koen Bossers]

By the way, adding time.sleep(11) before entering the loop eliminates the time differences
between outputs. They're nicely aligned at 0.2 secs. right now. Only that darned 10 second
pause....


Koen Bossers wrote:

> sill@optonline.net wrote:
>
> > Look at pctail.py program on vaults of parnassus, it does something
> similar
> > (reads from growing log files).
>
> Not what I had in mind. I want to avoid creating temporary files. That's
> why I
> chose popen, else I would have used something like os.system('command >>
>
> /tmp/tempfile') or something.
>
> OK second try: some VERY weird behaviour here:
>
> [print_messages.py]
> #! /usr/bin/python
>
> import time, os
>
> counter = 0
> while counter < 5000:
>
>     print '%d'%counter
>
>     time.sleep(0.01)
>     counter = counter + 1
>
> [popentest.py]
> #! /usr/bin/python
>
> ## test popen with continuing output
>
> import os, time, string
> import popen2
>
> child = popen2.Popen3('./print_messages.py')
> output = child.fromchild
>
> count = 1
>
> print "starting...", os.getpid()
> listing = ''
> start = time.time()
>
> while child.poll() == -1:        ## if child is still running...
>
>     print count, time.time()-start
>     test = output.read(100)
>
>     count = count + 1
>     time.sleep(0.2)
>
> output when i run popentest.py:
>
> starting... 414
> 1 after 0.000128984451294
> 2 after 10.696469903
> 3 after 10.896476984
> 4 after 11.0964080095
> 5 after 11.2964220047
> 6 after 11.4964289665
> 7 after 11.6964190006
> 8 after 11.8964159489
> 9 after 12.0963799953
> 10 after 12.2964549065
> 11 after 12.4964559078
> 12 after 12.6964579821
> 13 after 12.8963899612
> etc...
>
> Notice the major timediff between step 1 and 2! 10 seconds!!!! what the
> hell
> is happening here? I know Python isn't always that fast, but why this
> big
> delay? Enlighten me!
>
> Cheers,
>
> Koen Bossers
>