MetraPlot

#!/usr/bin/python3
# -*- coding: utf-8 -*-

'''
Simple demo program that reads the output of e.g. 'Metra'
and plots the measured values - either over time or by number.
It uses the extra python package 'matplotlib' for visualisation.
Install with: 'apt install python3-matplotlib' if missing.
'''

import sys
import argparse
import csv
import matplotlib.pyplot as plt


# create the parser
ap = argparse.ArgumentParser(description="Plot data - e.g. received from Gossen METRAHit 29S via program 'Metra'")

# add the arguments
ap.add_argument( '-t', '--title',
    action = 'store', default = 'MetraPlot',
    help = "set the title of the plot, default is 'MetraPlot'")
ap.add_argument( '-f', '--first_sample',
    action = 'store', type = int, default = 0,
    help = 'first sample to display')
ap.add_argument( '-l', '--last_sample',
    action = 'store', type = int, default = sys.maxsize,
    help = 'last sample to display')
ap.add_argument( '-V',
    action = 'count', dest = 'verbose', default = 0,
    help = 'increase verbosity' )
ap.add_argument( 'infile',
    type = argparse.FileType( 'r' ), nargs = '?', default = sys.stdin,
    help = 'read measurement data from optional infile, use stdin otherwise' )
# parse my argument
options = ap.parse_args()

# Use output of 'OpenMetra'
# Format: no header, values are SI units s and V, separated either by space or comma
# auto-detect the format
# detect also "german" csv (comma as decimal separator and semicolon as field separator)

one_line = options.infile.readline().rstrip('\n')    # get one line
options.infile.seek( 0 )                # and rewind the input

if options.verbose:
    print( '1st line: "', one_line, '"', sep='' )

time_unit = None
data_unit = None
time_index = None
data_index = None

# data file or csv file?
if ',' in one_line and '.' in one_line: # csv
    delim = ','
elif ';' in one_line:   # german csv
    delim = ';'
else:                   # data file
    delim = ' '
elements = one_line.split( delim )
num_elements = len( elements )
dec_sep = '.'
num_values = one_line.count( dec_sep )
if 0 == num_values and ',' != delim:    # german data or csv
    dec_sep = ','
    num_values = one_line.count( dec_sep )
if num_elements >= 4:   # "t.t 's' u.u 'V'"
    time_index = 0
    time_unit = elements[1]
    data_index = 2
    data_unit = elements[3]
elif num_elements >= 2:
    if num_values == 1: # "u.u 'V'"
        data_index = 0
        data_unit = elements[1]
    else:               # "t.t u.u"
        time_index = 0
        data_index = 1
else:                   # "u.u"
    data_index = 0

if options.verbose:
    print( "dec_sep: '", dec_sep, "', delim: '", delim, "'", sep='' )

if options.verbose > 1:
    print( "time_index: ", time_index, ", time_unit: '", time_unit,
          "', data_index: ", data_index, ", data_unit: '", data_unit, "'", sep='')

# process the data input
capture = csv.reader( options.infile, delimiter=delim )

# separate into one (data) or two (time, data) lists (plus number list)
numbers, time, data = [], [], []

number = -1
for row in capture:
    number += 1
    if len( row ) < num_elements: # incomplete row
        continue
    if time_index is not None:
        t = row[ time_index ]
        if '.' != dec_sep:  # german data
            t = t.replace( dec_sep, '.' )
        t = float( t )
        if round( t ) < options.first_sample:
            continue
        if round( t ) > options.last_sample:
            continue
        time.append( t )
    else:
        if number < options.first_sample:
            continue
        if number > options.last_sample:
            continue
    numbers.append( number )
    if data_index is not None:
        d = row[ data_index ]
        if '.' != dec_sep:
            d = d.replace( dec_sep, '.' )
        d = float( d )
        data.append( d )

options.infile.close()

if options.verbose > 1:
    print( 'numbers_size: ', len( numbers ), ', time_size: ', len( time ), ', data_size: ', len( data ), sep='' )

if data_unit is None:
    data_unit = 'Value'

# prepare a nice picture with the help of 'matplotlib.pyplot'
figure, measure = plt.subplots( 1 )

measure.set_title( options.title )

if len( time ):
    measure.plot( time, data )
    xl = 'Time (s)'
else:
    measure.plot( numbers, data )
    xl = 'N'

measure.set(xlabel=xl, ylabel=data_unit )
measure.grid( True )

# arrange layout for good readability
figure.tight_layout()

# display everything
plt.show()