hardcopy of gnuplot.py plot

Thats, what the command set size is for: Change the plot size relative to the total canvas/image size. In order to change the image size, you must use the size parameter of the set terminal command. Unfortunately, that is not supported by some terminals which are defined in termdefs.py of gnuplot-py. As the comment in termdefs.py says:

"""Terminal definition file.

This module describes the options available to gnuplot's various terminals. For the moment, it only supports a few terminals, but the infrastructure is here to add others as they are needed. ...

The svg terminal supports the size parameter:

import Gnuplot
from numpy import *

x1 = arange(1,10)
y1 = arange(1,10)

d1 = Gnuplot.Data(x1,y1, with_="lines lt rgb 'red'", title="1")
g = Gnuplot.Gnuplot()

g.title("aaa")
g('set grid')
g('set logscale x')
g('set xtics 1,2,110')
g.plot(d1)
g.hardcopy("aaa.svg", terminal='svg', size=[800,400])

The most flexible way is to pass the raw terminal definition string to gnuplot. Then, the line g.hardcopy... becomes:

g('set terminal pngcairo size 800,400')
g.set_string('output', 'aaa.png')
g.refresh()
g.set_string('output')

That allows you also to use the better pngcairo terminal instead of the png terminal.