Plotting with gnuplot via Python

plot_gnuplot.py

#!/usr/bin/env python

"""
This example shows how to call gnuplot from Python

It uses Popen() from the subprocess module.
The function run_gnuplot() takes care of it and returns the
resulting image as bytes. If you run this code on a web server,
the result could be returned to the client without storing
a file on the disk. In this example it is saved to a file in the end.
"""

from subprocess import Popen, PIPE
import sys
from os import linesep as nl
import logging
import itertools
import random

logger = logging.getLogger(__name__)
logging.basicConfig(level=logging.WARNING)

def run_gnuplot(commands, data, persist=True):
    """ Return the output of a gnuplot command """
    args = ["gnuplot", ]
    if persist:
        args.append("-persist")
    args.append("-e")
    args.append("; ".join([str(c) for c in commands]))
    logger.info('args: {}'.format(args))
    in_pipe, out_pipe, err_pipe = PIPE, PIPE, PIPE
    gnuplot = Popen(args, stdin=in_pipe, stdout=out_pipe, stderr=err_pipe)
    logger.info('data: {}'.format(nl.join(data).encode('ascii')))
    out, err = gnuplot.communicate(nl.join(data).encode('ascii'))
    logger.debug('out: {}'.format(out))
    if err:
        logger.error('err: {}'.format(err))
    if err:
        raise NameError('There was a problem with the gnuplot commands or data: ' + err.decode('ascii'))
    if gnuplot.returncode != 0:
        raise NameError('The returncode of gnuplot was not zero but {}. There was a problem with the gnuplot commands or data.'.format(gnuplot.returncode))
    return out

def gnuplot_scope(all_data, context):
    """
    all_data contains the list of data sets (list of lists)
    context is a dictionary with contextual information for the plot
    """
    commands = [
        "set title '{title}'",
        "set term {format} size {size}",
        "set key left",
        "set yrange [{ymin}:{ymax}]",
        "set xrange [0:1200]",
        "set xtics {tics}",
        "set xlabel ' Time {timescale} {tu} per div'",
        "set ylabel ' Voltage in V'",
        "set grid",
        "set object 1 rect from screen 0, 0, 0 to screen 1, 1, 0 behind",
        "set object 1 rect fc  rgb {bgcolor}  fillstyle solid 1.0",
        "set datafile separator ','",
        "set output",
        ]
    commands = [cmd.format(**context) for cmd in commands]
    data_lines = []
    i = 0
    plot_commands = []
    for chan_data in all_data:
        logger.info('preparing {} - {}'.format(i, context['channels'][i]))
        plot_commands.append("'{source}' using 1 with lines title '{name}'".format(source=('-' if i==0 else ''), name=context['channels'][i]))
        data_lines += [str(val) for val in chan_data] + ['e']
        i += 1
    commands += ['plot' + ', '.join(str(c) for c in plot_commands)]
    return (commands, data_lines)

if __name__ == "__main__":
    context = {}
    context['title'] = 'Your Scope'
    context['channels'] = ['CHAN1', 'CHAN2']
    context['format'] = 'png' # or 'svg'
    context['size'] = '1000,640'
    context['bgcolor'] = '"white"' # or '"gray"'
    alldata = []
    for channel in context['channels']:
        values = itertools.accumulate([random.uniform(-0.05, 0.05) for i in range(1200)])
        alldata.append(list(values))
    min_value = min(min(samples) for samples in alldata)
    max_value = max(max(samples) for samples in alldata)
    context['ymin'] = min_value - 0.1 * (max_value - min_value)
    context['ymax'] = max_value + 0.2 * (max_value - min_value)
    context['tics'] = '(' + ', '.join(str(i*100) for i in range(1, 12)) + ')'
    context['timescale'] = float('100e-6')
    context['tu'] = 's'

    (commands, data_lines) = gnuplot_scope(alldata, context)
    gnuplot_output = run_gnuplot(commands, data_lines, persist=False)
    filename = 'tmp.png'
    with open(filename, 'wb') as f:
        f.write(gnuplot_output)
    print("Wrote {}!".format(filename))