test for custom line renderer not rendering the entire line contents

test.py

#!/usr/bin/env python

import sys
from gi.repository import Gtk
from gi.repository import GtkSource

class CustomLineRenderer(GtkSource.GutterRendererText):
    line_offset = 0

    def __init__(self, start_line, *args, **kwargs):
        self.line_offset = start_line
        GtkSource.GutterRendererText.__init__(self, *args, **kwargs)

    def do_query_data(self, start, end, flags):
        self.props.text = str(start.get_line() + self.line_offset + 1)
        width, height = self.measure(self.props.text)
        if self.props.size < width:
            self.props.size = width

def main(filename, start_line, end_line):
    win = Gtk.Window(default_width=800, default_height=300)

    scroller = Gtk.ScrolledWindow(visible=True)
    win.add(scroller)

    textbuffer = GtkSource.Buffer()
    textbuffer.set_text(''.join(file(filename).readlines()[start_line:end_line]))
    textview = GtkSource.View(visible=True, buffer=textbuffer, monospace=True, editable=False)
    scroller.add(textview)

    gutter = textview.get_gutter(Gtk.TextWindowType.LEFT)

    renderer = CustomLineRenderer(start_line, xpad=6, xalign=1.0)
    gutter.insert(renderer, 0)

    win.present()
    win.connect('delete-event', lambda *_: Gtk.main_quit())
    Gtk.main()

    return 0

if __name__ == '__main__':
    if len(sys.argv) < 4:
        print >> sys.stderr, "usage: %s filename start_line end_line" % sys.argv[0]
        sys.exit(1)

    filename, start, end = sys.argv[1:4]
    sys.exit(main(filename, int(start)-1, int(end)-1))