[Tutor] "standard output: Broken pipe"

[James]

It seems that adding this line:

signal.signal(signal.SIGPIPE, signal.SIG_DFL)

Before the snippet of code I included in my original e-mail  
(subprocess.call( "yes '' | make oldconfig" , shell=True )) got rid  
of the error.  I can't seem to figure out precisely what the  
signal.signal() function does (as shown above).

Any ideas?  I'd like to fully understand what it does before I add it  
to my program.  :)

Thanks!
.james

On Oct 20, 2007, at 5:42 AM, Martin Walsh wrote:

> James wrote:
>> Hi,
>>
>> I have a snippet of code in a Python script I'm whipping up that's
>> causing a not-so-pretty output.  Here's the code:
>>
>> subprocess.call( "yes '' | make oldconfig" , shell=True )
>>
>> When I run this code, Python loyally executes the command, and then I
>> see the following error on my console:
>>
>> -----
>>
>> yes: standard output: Broken pipe
>> yes: write error
>>
>> Thoughts / ideas?
>
> File this one under 'wicked scary hack', but my first thought would be
> to redirect stderr of 'yes' to /dev/null, while preserving stderr of
> 'make oldconfig'. Something like this:
>
> import subprocess as sp
> sp.call("yes '' 2> /dev/null | make oldconfig", shell=True)
>
> ... or ...
>
> import subprocess as sp
> p1 = sp.Popen("yes ''", shell=True, stdout=sp.PIPE,
>          stderr=file('/dev/null', 'w'))
> p2 = sp.Popen('make oldconfig', shell=True,
>          stdin=p1.stdout)
>
> However, since the 'equivalent' shell command doesn't seem to  
> result in
> a broken pipe error there must be a better way. Upon further  
> inspection:
>
>   $ strace yes 'Spam' | head -n 10
>   <...>
>   --- SIGPIPE (Broken pipe) @ 0 (0) ---
>   +++ killed by SIGPIPE +++
>   <...>
>
> We may need to handle SIGPIPE. A quick search leads here:
> http://article.gmane.org/gmane.comp.python.devel/88798/
>
> ... so, thanks to Mr. Woodcraft ...
>
> import subprocess as sp
> import signal
> # warning: uses the system default action
> # for SIGPIPE for all children, use subprocess
> # preexec_fn arg if this is not desirable
> signal.signal(signal.SIGPIPE, signal.SIG_DFL)
> sp.call("yes 'Spam' | head -n 10", shell=True)
>
> HTH,
> Marty
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