pseudo terminal usage from Python?

Steve Holden steve at holdenweb.com
Tue Dec 23 15:21:13 CET 2008


skip at pobox.com wrote:
> I ran into an interesting problem yesterday.  The mpstat(1) command on
> Solaris formats its output like so:
> 
>   CPU minf mjf xcal  intr ithr  csw icsw migr smtx  srw syscl  usr sys  wt idl
>     0   42   1 1184   812  265  227   12   44   37    0  1131    6   2   0  93
>     1   25   1  933   447    2  203   37   75   12    0   902    5   4   0  91
>     2   17   0  195   495    1  201   41   77   13    0   514    5   1   0  94
>     3    4   0  117   882  405  171   34   65   21    0   449    5   2   0  93
> 
> I'm only interested in presenting the CPU numbers and user+sys values
> prefixed by a timestamp.  For example, the above might be formatted like so:
> 
>     07:28:46.373328 0 8 1 9 2 6 3 7
> 
> The obvious solution might be something simple like this:
> 
>     mpstat 1 | python mympstat.py
> 
> where mympstat.py does a trival amount of reformatting.
> 
> The problem is that mpstat recognizes when its output is a pipe and block
> buffers it so the Python script sees input in massive blobs, not the
> second-by-second output you'd see running "mpstat 1" by itself.  I've been
> reduced to a much more complicated solution which involves forking mpstat
> with output to a file, then reading the end of that file every second.  A
> three-line Python script balloons into a one-page script.  Yuck.  Add to
> that I'm writing this for an admin who is considering Python as a scripting
> language.   Double Yuck.  (But not nyuk nyuk, this is not the Stooges.)
> 
> I suspect there is some magic I can perform with pseudo terminals (this is
> on Solaris 10.)  The documentation for the pty module contains no examples
> and I've been so far unable to find any using Google.
> 
> Any pointers/examples?  I will gladly add an example to the pty module docs
> (I have the power!) once I have a couple working examples (maybe one example
> each of reading and writing?)
> 
Look at the pexpect module - you can run interactive tasks through that.

regards
 Steve
-- 
Steve Holden        +1 571 484 6266   +1 800 494 3119
Holden Web LLC              http://www.holdenweb.com/




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