Plot metl schema XML using Matplotlib to produce a PNG

plot.py

#!/usr/bin/env python2
'''
Plots a MELT xml schema with matplotlib
'''
from __future__ import print_function
from lxml import etree
import sys
from datetime import datetime, timedelta
from matplotlib.backends.backend_agg import FigureCanvasAgg as FigureCanvas
from matplotlib.figure import Figure

# JS like object access for dicts
try:
    from bunch import Bunch
except ImportError:
    print("please install bunch to run this command")
    sys.exit(1)
# Easy argparse alternative
try:
    import click
except ImportError:
    print("please install click to run this command")
    sys.exit(1)


def _dbg(e):
    '''Display etree to stdout'''
    print(etree.tostring(e, pretty_print=True))


def seconds(secs):
    '''Time delta in seconds. Accepts strings'''
    if isinstance(secs, basestring):
        secs = float(secs)
    return timedelta(seconds=secs)


def get_musix_xy(music_prod, base_time=None):
    points = []
    # Go through music
    for flt in music_prod.xpath('./filter'):
        gain = flt.find('./property[@name="gain"]')
        end = flt.find('./property[@name="end"]')
        in_ = float(flt.attrib['in'])
        out = float(flt.attrib['out'])

        start = (base_time + seconds(in_), float(gain.text))
        end = (base_time + seconds(out), float(end.text))

        points.append(start)
        points.append(end)

    # Sort
    points.sort(cmp=lambda a, b: cmp(a[0], b[0]))
    x = [e[0] for e in points]
    y = [e[1] for e in points]
    return x, y


def plot_schema(xml_schema):
    """Converts schema into plot"""
    music_prod = xml_schema.xpath('//producer[contains(@id,"music")]')[0]

    fig = Figure()
    ax = fig.add_subplot(111)

    # We need a datetime to do timedelta cacls
    base_time = datetime(1970, 1, 1)

    # Draw palylist

    max_out_time = base_time

    for i, plst in enumerate(xml_schema.xpath('//playlist')):
        data = Bunch(plst.attrib)               # Adds Id, autoclose
        try:
            data.update(plst.find('blank').attrib)  # Adds length
        except AttributeError:
            data.update({'length': 0})
        data.update(plst.find('entry').attrib)  # Adds in and out

        if 'music' in data.id:  # lousy comparision

            offsetd_time = base_time + seconds(data.length)
            music_prod = xml_schema.xpath('//producer[@id="%s"]' % data.producer)[0]
            x, y = get_musix_xy(music_prod, base_time=offsetd_time)
            ax.plot_date(x, y, '-', label='audio volume')
        else:
            in_time = base_time + seconds(data.length) + seconds(data['in']) # In resvd
            out_time = base_time + seconds(data.length) + seconds(data.out)
            x = [in_time - seconds(-0.01), in_time, out_time, out_time + seconds(0.01)]
            y = [0, 1, 1, 0]
            ax.plot_date(x, y, '-', label=data.id)
            if out_time > max_out_time:
                max_out_time = out_time

    # The following two lines could be improved if there's no space left for
    # lables
    ax.axis([base_time, max_out_time, 0, 1.1 + 2])
    ax.legend()
    fig.autofmt_xdate()
    #import ipdb; ipdb.set_trace()

    canvas = FigureCanvas(fig)
    return canvas

@click.command()
@click.argument('paths', nargs=-1)
@click.argument('dst', nargs=1, default='-')
def main(paths, dst):
    print(dst)
    if not paths and dst:
        paths = [dst, ]
        dst = 'output.png'

    for p in paths:
        click.echo("Processing {}".format(p), file=sys.stderr)
        with open(p) as fp:
            xml = etree.fromstring(fp.read())

        canvas = plot_schema(xml)

        click.echo("Writing output to {}".format(dst), file=sys.stderr)
        canvas.print_png(dst)

if __name__ == '__main__':
    main()