read stdout/stderr without blocking

[Jacek Popławski]

Grant Edwards wrote:
> You're right.  I must have been remembering the behavior of a
> network socket.  Apparently, you're supposed to read a single
> byte and then call select() again.  That seems pretty lame.

I created another thread with single read(), it works, as long as I have 
  only one PIPE (i.e. stderr is redirected into stdout).
I wonder is it Python limitation or systems one (I need portable solution)?