[Tutor] Interacting with stderr

[Danny Yoo]

>> Rather than construct the pipeline through the shell, do it through
>> Python if you can.  See:
>>
>> https://docs.python.org/2/library/subprocess.html#replacing-shell-pipeline
>
> But his use case is not using a shell pipeline, so irrelevant. It just makes
> things more complex for him.


Did I misread the code?  Here's the snippet I thought was part of the question:

>>       p = subprocess.call("avconv -v verbose -re -analyzeduration 1000 -ihttp://localhost:6498/ms2/1382097438004/0MediaPlayer+0+/octoshape+hVV+octolive.americaone.com+V+aone+V+live+V+ONECONNXT_DEMO1_HD_flv/aoneliveONECONNXTDEMO1HDflv -c:v rawvideo -c:a pcm_s16le -ar 48000 -f nut - | ./bmdplay -m 12 -f pipe:0",
> shell=True)

where there's a pipeline between the avconv process mbdplay process.



> Again, disagree. In this specific case, disagree strongly.
>
> Firstly, the OP is not feeding stuff to stdin nor collecting stdout.
>
> Secondly, the OP has made it clear that they're not in a position to wait
> for the command to finish; they need to read stderr as it occurs because the
> run time is very long and they need to act earlier than process completion.

The OP's situation is somewhat unusual.  My apologies for not reading
the thread thoroughly and closely.  I got distracted by the initial
digest message.


> Thirdly, I generally consider advice to use .communicate bad advise.
>
> .communicate has many potential issues:
>
> Primarily, it hides all the mechanics. He will learn nothing.


If it helps, let me qualify the statement that communicate() is
usually an appropriate solution.  For simple, common cases where the
interaction isn't that large or long-running, Popen.communicate() is
probably the right tool.  That is, I would usually recommend
Popen.communicate() _unless_ the details made it the wrong tool.  I
misread the problem statement, so yeah, my bad.

The OP's requirements are unusual: it's a long running process, it's
generating a dynamic, large amount of stderr output, it's disregarding
stdout, and there's a desire to process the stderr on the fly.  In
that situation, your solution sounds reasonable.