Connecting to gnuplot with Popen?

[Anton81]

Hi,

it seems to be a FAQ, but I still haven't found a solution. I want to
control gnuplot with a python program. The following at least gives me the
gnuplot output:

subp=Popen("gnuplot",stdin=None,stderr=PIPE,stdout=PIPE)
...
subp.stderr.readline()

even though I'm not sure how to check if no more lines can be read with
readline() so that it doesn't block.
But after the script has finished, the console doesn't show me the
characters I type.

However, as soon as I try:

subp=Popen("gnuplot",stdin=PIPE,stderr=PIPE,stdout=PIPE)
...
subp.stderr.readline()

the program hangs.

What's wrong?

Anton