[Tutor] Newbie Wondering About Threads

[Damon Timm]

On Sat, Dec 6, 2008 at 6:25 PM, Python Nutter <pythonnutter at gmail.com> wrote:
> I'm on my phone so excuse the simple reply.
> From what I skimmed you are wrapping shell commands which is what I do
> all the time. Some hints. 1) look into popen or subprocess in place of
> execute for more flexibility. I use popen a lot and assigning a popen
> call to an object name let's you parse the output and make informed
> decisions depending on what the shell program outputs.

So I took a peak at subprocess.Popen --> looks like that's the
direction I would be headed for parallel processes ... a real simple
way to see it work for me was:

p2 = subprocess.Popen(["lame","--silent","test.wav","test.mp3"])
p3 = subprocess.Popen(["lame","--silent","test2.wav","test2.mp3"])
p2.wait()
p3.wait()

top showed that both cores get busy and it takes half the time!  So
that's great -- when I tried to add the flac decoding through stdout I
was able to accomplish it as well ... I was mimicing the command of
"flac --decode --stdout test.flac | lame - test.mp3" ... see:

p = subprocess.Popen(["flac","--decode","--stdout","test.flac"],
stdout=subprocess.PIPE)
p2 = subprocess.Popen(["lame","-","test.mp3"], stdin=subprocess.PIPE)
p2.communicate(p.communicate()[0])

That did the trick - it worked!  However, it was *very* slow!  The
python script has a "real" time of 2m22.504s whereas if I run it from
the command line it is only 0m18.594s.  Not sure why this is ...

The last piece of my puzzle though, I am having trouble wrapping my
head around ... I will have a list of files
["file1.flac","file2.flac","file3.flac","etc"] and I want the program
to tackle compressing two at a time ... but not more than two at a
time (or four, or eight, or whatever) because that's not going to help
me at all (I have dual cores right now) ... I am having trouble
thinking how I can create the algorithm that would do this for me ...

Thanks everyone.  Maybe after a good night's sleep it will come to me.
 If you have any ideas - would love to hear them.

Damon