[Tutor] Interacting with stderr
Crush
crushed26 at gmail.com
Thu Aug 28 02:28:58 CEST 2014
As far as sending the contents of stderr to a tmp file...hmmm, i will try that. My only concern is, many of these systems run live demo feeds for many days...10+. Im afraid the file will fill up very quickly and present problems.
Stderr=PIPE causes the terminal to hang. I can not wait for the process to terminate, i need to read stderr as it is being fed data.. Would fifos be of any use here?
I will research the tempfile module.
Bo
> On Aug 27, 2014, at 7:38 PM, tutor-request at python.org wrote:
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> Today's Topics:
>
> 1. Re: Python Programming (Alan Gauld)
> 2. Re: simple unicode question (Alan Gauld)
> 3. Interacting with stderr (Crush)
> 4. Re: Interacting with stderr (Cameron Simpson)
> 5. Re: debug and execute python code in Mac (Alan Gauld)
> 6. Re: Interacting with stderr (Alan Gauld)
>
>
> ----------------------------------------------------------------------
>
> Message: 1
> Date: Wed, 27 Aug 2014 19:57:12 +0100
> From: Alan Gauld <alan.gauld at btinternet.com>
> To: tutor at python.org
> Subject: Re: [Tutor] Python Programming
> Message-ID: <ltl9m8$m45$1 at ger.gmane.org>
> Content-Type: text/plain; charset=windows-1252; format=flowed
>
>> On 27/08/14 14:40, Jake wrote:
>> To whom it may concern,
>> My name is Jake and I have recently started the GCSE computing course with school.
>
>> answera = input()
>> if answera == ["Oslo" or "oslo"]:
>
> This doesn't do what you think it does.
>
> ["Oslo" or "oslo"] is a list
>
> "Oslo" or "oslo" is the content of the list and
> is a boolean expression which evaluates to True.
> (Each non-empty string is considered True by Python)
>
> So your 'if' line looks to Python like:
>
> if answera == [True]:
>
> But answera is a string so it will never equal a list
> with a single boolean value so you go to the else
> clause.
>
> A better way to do what you want is to convert the input
> to lowercase using the string lower() method and compare
> that to the string you want, like so:
>
> if answera.lower() == "oslo":
>
> If you need to check multiple possible answers you can use
> a list of strings and the 'in' operator like this:
>
> if answera.lower() in ['amsterdam', 'london', 'oslo']:
>
> HTH
> --
> Alan G
> Author of the Learn to Program web site
> http://www.alan-g.me.uk/
> http://www.flickr.com/photos/alangauldphotos
>
>
>
> ------------------------------
>
> Message: 2
> Date: Wed, 27 Aug 2014 20:09:36 +0100
> From: Alan Gauld <alan.gauld at btinternet.com>
> To: tutor at python.org
> Subject: Re: [Tutor] simple unicode question
> Message-ID: <ltladg$uva$1 at ger.gmane.org>
> Content-Type: text/plain; charset=utf-8; format=flowed
>
> On 27/08/14 15:57, Albert-Jan Roskam wrote:
>
>>> if *fewer* than 1 in 10 operations will raise an exception, then use
>>> try...except; but if *more* than 1 in 10 operations will raise an
>>> exception, and it is safe to do so, then LBYL may be appropriate.
>>
>>
>> Thanks a lot, Steven! This kind of stuff should be in a book.
>
> It is in lots of books but they aren't Python books; they are generic
> software engineering books. Because this is not really a language
> specific type design issue, its general software design.
>
>> Do you know of any real life examples where the code is written
>> in such a way that it could switch from AFTP to LBYL
>
> It would be very unlikely since it would almost always be a case of
> premature optimisation. You would need to be inside a very tight loop to
> make that kind of optimisation worthwhile in real world scenarios.
> (And the cost of evaluating it would probably outweigh any gains.)
>
> Much more important is to make the code correct and maintainable than to
> worry about slight performance issues before they are a proven issue.
> Building those kind of self modifying control flows makes code much more
> error prone and difficult to modify.
>
> The vast majority of performance issues in software are to do with
> blockages in IO processing(network, disk access, human input, etc)
> or database processing (big data or complex searches) or in traversing
> complex/deep data structures. Very few real-world performance issues
> are related to simple code execution issues.
>
> --
> Alan G
> Author of the Learn to Program web site
> http://www.alan-g.me.uk/
> http://www.flickr.com/photos/alangauldphotos
>
>
>
> ------------------------------
>
> Message: 3
> Date: Wed, 27 Aug 2014 18:45:41 -0400
> From: Crush <crushed26 at gmail.com>
> To: "tutor at python.org" <tutor at python.org>
> Subject: [Tutor] Interacting with stderr
> Message-ID: <77745CA4-8F7D-410C-800D-F0A3C711D2F2 at gmail.com>
> Content-Type: text/plain; charset="us-ascii"
>
> Hello, it has been a while and I hope I am sending to the correct email.
>
> How would I go about running a conditional statement against the contents of stderr. For instance, if "blah blah blah" is in stderr do X, else do Y.
>
> CODE: SELECT ALL
>
> #!/usr/bin/env python
> import subprocess
> from subprocess import PIPE
> i = 0
> while i < 10:
> p = subprocess.call("avconv -v verbose -re -analyzeduration 1000 -i http://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)
> i += 1
> if i == 10:
> print "Gave up"
>
>
> The above code works and I get no tracebacks, however I need to add to it and check the contents of stderr. Avconv by default sends the audio and video to stdout, which then sends the signal to a capture card in the machine. Avconv is sending the status of the broadcasted signal i.e. frames, time, fps, etc. to stderr, which is displayed in the terminal.
>
> Bo
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> ------------------------------
>
> Message: 4
> Date: Thu, 28 Aug 2014 08:55:39 +1000
> From: Cameron Simpson <cs at zip.com.au>
> To: "tutor at python.org" <tutor at python.org>
> Subject: Re: [Tutor] Interacting with stderr
> Message-ID: <20140827225539.GA55624 at cskk.homeip.net>
> Content-Type: text/plain; charset=us-ascii; format=flowed
>
>> On 27Aug2014 18:45, Crush <crushed26 at gmail.com> wrote:
>> Hello, it has been a while and I hope I am sending to the correct email.
>>
>> How would I go about running a conditional statement against the contents of
>> stderr. For instance, if "blah blah blah" is in stderr do X, else do Y.
>>
>>
>> #!/usr/bin/env python
>> import subprocess
>> from subprocess import PIPE
>> i = 0
>> while i < 10:
>> p = subprocess.call("avconv -v verbose -re -analyzeduration 1000 -i http://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)
>> i += 1
>> if i == 10:
>> print "Gave up"
>>
>> The above code works and I get no tracebacks, however I need to add to it and
>> check the contents of stderr. Avconv by default sends the audio and video to
>> stdout, which then sends the signal to a capture card in the machine. Avconv
>> is sending the status of the broadcasted signal i.e. frames, time, fps, etc.
>> to stderr, which is displayed in the terminal.
>
> Send stderr to a file, using a parameter like:
>
> stderr=open('stderr.out', 'w')
>
> in your call() call. Then open 'stderr.out' and look for the relevant
> information.
>
> Obviously in a "real" program you'd take care to make that a temporary file
> with a unique name using the functions from the "tempfile" module, etc. But
> make it work first.
>
> Cheers,
> Cameron Simpson <cs at zip.com.au>
>
> The Few. The Proud. The Politically Incorrect. - Steve Masticola
>
>
> ------------------------------
>
> Message: 5
> Date: Thu, 28 Aug 2014 00:31:08 +0100
> From: Alan Gauld <alan.gauld at btinternet.com>
> To: tutor at python.org
> Subject: Re: [Tutor] debug and execute python code in Mac
> Message-ID: <ltlpns$sic$1 at ger.gmane.org>
> Content-Type: text/plain; charset=windows-1252; format=flowed
>
> On 27/08/14 13:47, Patrick Thunstrom wrote:
>
>>> I do not like the cmd/terminal execution. Thanks !
>>
>> I don't know many ways to debug code that don't involve the terminal
>> in some fashion. Even with a good IDE you're going to have a terminal
>> built in for output.
>
> Not necessarily. A text display widget within a GUI is very different
> from a text based terminal. Many graphical debuggers display data
> structures in a hierarchical model where you can expand/close the
> various levels etc.
>
> But I think the OP is specifically wanting to avoid command prompts. The
> question is: Does he mean all prompts (including
> Python's) or just the OS prompt? If its all prompts then it gets
> much harder to find an IDE that will suit.
>
>
> --
> Alan G
> Author of the Learn to Program web site
> http://www.alan-g.me.uk/
> http://www.flickr.com/photos/alangauldphotos
>
>
>
> ------------------------------
>
> Message: 6
> Date: Thu, 28 Aug 2014 00:38:09 +0100
> From: Alan Gauld <alan.gauld at btinternet.com>
> To: tutor at python.org
> Subject: Re: [Tutor] Interacting with stderr
> Message-ID: <ltlq51$v4s$1 at ger.gmane.org>
> Content-Type: text/plain; charset=windows-1252; format=flowed
>
>> On 27/08/14 23:45, Crush wrote:
>> Hello, it has been a while and I hope I am sending to the correct email.
>>
>> How would I go about running a conditional statement against the
>> contents of stderr. For instance, if "blah blah blah" is in stderr do X,
>> else do Y.
>
> You can access stderr just like you access stdout.
> The recommended way is via communicate:
>
> ---------------
> Popen.communicate(input=None, timeout=None)
>
> Interact with process: Send data to stdin. Read data from stdout and
> stderr, until end-of-file is reached. Wait for process to terminate. The
> optional input argument should be data to be sent to the child process,
> or None, if no data should be sent to the child. The type of input must
> be bytes or, if universal_newlines was True, a string.
>
> communicate() returns a tuple (stdoutdata, stderrdata).
>
> Note that if you want to send data to the process?s stdin, you need to
> create the Popen object with stdin=PIPE. Similarly, to get anything
> other than None in the result tuple, you need to give stdout=PIPE and/or
> stderr=PIPE too.
> --------------------
>
> HTH
> --
> Alan G
> Author of the Learn to Program web site
> http://www.alan-g.me.uk/
> http://www.flickr.com/photos/alangauldphotos
>
>
>
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>
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