Raising exception on STDIN read

[Gabriel Genellina]

En Thu, 28 Feb 2008 14:29:04 -0200, Ian Clark <iclark at mail.ewu.edu>  
escribió:

> On 2008-02-27, Gabriel Genellina <gagsl-py2 at yahoo.com.ar> wrote:
>> En Wed, 27 Feb 2008 15:06:36 -0200, Ian Clark <iclark at mail.ewu.edu>
>> escribi�:
>>
>>> On 2008-02-27, Michael Goerz <newsgroup898sfie at 8439.e4ward.com> wrote:
>>>> Hi,
>>>>
>>>> I would like to raise an exception any time a subprocess tries to read
>>>> from STDIN:
>>>>
>>>> latexprocess = subprocess.Popen( \
>>>>          'pdflatex' + " " \
>>>>           + 'test' + " 2>&1", \
>>>>          shell=True, \
>>>>          cwd=os.getcwd(), \
>>>>          env=os.environ, \
>>>>          stdin=StdinCatcher() # any ideas here?
>>>>      )
>>>>
>>>> An exception should be raised whenever the pdflatex process
>>>> reads from STDIN... and I have no idea how to do it. Any suggestions?
>>
>>> How about with a file-like object? I haven't tested this with  
>>> subprocess
>>> so you might want to read the manual on files if it doesn't work[1].
>>
>> Won't work for an external process, as pdflatex (and the OS) knows  
>> nothing
>> about Python objects. The arguments to subprocess.Popen must be actual
>> files having real OS file descriptors.
>
> Taken from the subprocess documentation (emphasis mine). [1]
>
> 	stdin, stdout and stderr specify the executed programs' standard
> 	input, standard output and standard error file handles,
> 	respectively. Valid values are PIPE, an existing file descriptor (a
> 	positive integer), *an existing file object*, and None.
>
> The following peice of code works fine for me with the subprocess
> module. NOTE: the only difference from this and the last I posted is
> that I set fileno() to _error().
>
>     import sys
>     import subprocess
>
>     class ErrorFile(object):
>         def _error(self, *args, **kwargs):
>             raise AssertionError("Illegal Access")
>
>         def _noop(self, *args, **kwargs):
>             pass
>
>         close = flush = seek = tell = _noop
>         next = read = readline = readlines = xreadlines = tuncate =  
> _error
>         truncate = write = writelines = fileno = _error
>         #                               ^^^^^^
>
>     proc = subprocess.Popen("cat -", shell=True, stdin=ErrorFile())
>     ret = proc.wait()
>     print "return", ret

I don't see how this could ever work. The shell knows nothing about your  
ErrorFile objects. If subprocess.Popen doesn't reject that ErrorFile  
instance, it's a bug. An ErrorFile instance is not "an existing file  
object".


-- 
Gabriel Genellina