polling for output from a subprocess module

Thomas Bellman bellman at lysator.liu.se
Wed Feb 6 08:18:35 CET 2008

Ivo <noreply at ivonet.nl> wrote:

> Thomas Bellman wrote:

>> However, the os.read() function will only read what is currently
>> available.  Note, though, that os.read() does not do line-based
>> I/O, so depending on the timing you can get incomplete lines, or
>> multiple lines in one read.
> be carefull that you specify how much you want to read at a time, 
> otherwise it cat be that you keep on reading.

> Specify read(1024) or somesuch.

Well, of course you need to specify how much you want to read.
Otherwise os.read() throws an exception:

    >>> import sys, os
    >>> os.read(sys.stdin.fileno())
    Traceback (most recent call last):
      File "<stdin>", line 1, in <module>
      TypeError: read() takes exactly 2 arguments (1 given)

> In case of my PPCEncoder I recompiled the mencoder subprocess to deliver 
> me lines that end with \n.

> If anyone can tell me how to read a continues stream than I am really 
> interested.

I have never had any problem when using the os.read() function,
as long as I understand the effects of output buffering in the
subprocess.  The file.read() method is a quite different animal.

(And then there's the problem of getting mplayer/mencoder to
output any *useful* information, but that is out of the scope of
this newsgroup. :-)

Thomas Bellman,   Lysator Computer Club,   Linköping University,  Sweden
"God is real, but Jesus is an integer."      !  bellman @ lysator.liu.se
                                             !  Make Love -- Nicht Wahr!

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