Controlling gnuplot via subprocess.Popen

[Ben C]

On 2007-04-25, Peter Beattie <Peter.Beattie at web.de> wrote:
> I am trying to plot something in gnuplot 4.2 using co-ordinates a Python
> 2.5 program computes. Here's what I'm doing:
>
> py> from subprocess import *
> py> plot = Popen("c:/progs/gp/bin/wgnuplot.exe", stdin=PIPE)
> py> plot.stdin.write("plot x*x")
>
> The first command dutifully opens gnuplot, but the second doesn't do
> anything. Could someone favour me with an explanation as to the whyness?

I think it may just be that you need a newline after "plot x*x", i.e.

    plot.stdin.write("plot x*x\n")

or

    print >>plot.stin, "plot x*x"

But some interactive programs need to be controlled with expect rather
than just writing to their stdin. I'm unclear of the details, perhaps
it's just ones that use curses in some form.

I usually write the gnuplot commands to a file, and then use
os.system("gnuplot plot.gpi") to run gnuplot in batch mode (or gnuplot
-persist if you want the window). You can also use Popen instead of
os.system.