What does canon do?

lib/python/qt5_graphics.py:392:            result, seq = self.load_preview(filename, canon, unitcode, initcode)

    def load(self,filename = None):
        s = self.stat
        s.poll()
        if not filename and s.file:
            filename = s.file
        elif not filename and not s.file:
            return


        lines = open(filename).readlines()
        progress = Progress(2, len(lines))
        # monkey patch function to call ours
        progress.emit_percent = self.emit_percent

        code = []
        i = 0
        for i, l in enumerate(lines):
            l = l.expandtabs().replace("\r", "")
            code.extend(["%6d: " % (i+1), "lineno", l, ""])
            if i % 1000 == 0:
                del code[:]
                progress.update(i)
        if code:
            pass
        progress.nextphase(len(lines))


        td = tempfile.mkdtemp()
        self._current_file = filename
        try:
            random = int(self.inifile.find("EMCIO", "RANDOM_TOOLCHANGER") or 0)
            arcdivision = int(self.inifile.find("DISPLAY", "ARCDIVISION") or 64)
            text = ''
            canon = StatCanon(self.colors,
                                self.get_geometry(),
                                self.foam_option,
                                self.lathe_option,
                                s, text, random, i,
                                progress, arcdivision)
            # monkey patched function to call ours
            canon.output_notify_message = self.output_notify_message
            parameter = self.inifile.find("RS274NGC", "PARAMETER_FILE")
            temp_parameter = os.path.join(td, os.path.basename(parameter or "linuxcnc.var"))
            if parameter:
                shutil.copy(parameter, temp_parameter)
            canon.parameter_file = temp_parameter
            unitcode = "G%d" % (20 + (s.linear_units == 1))
            initcode = self.inifile.find("RS274NGC", "RS274NGC_STARTUP_CODE") or ""
            result, seq = self.load_preview(filename, canon, unitcode, initcode)
            if result > gcode.MIN_ERROR:
                self.report_gcode_error(result, seq, filename)
            self.logger.set_depth(self.from_internal_linear_unit(self.get_foam_z()),
                       self.from_internal_linear_unit(self.get_foam_w()))
            self.calculate_gcode_properties(canon)
        except Exception as e:
            print (e)
            self.gcode_properties = None
        finally:
            shutil.rmtree(td)
            if canon:
                canon.progress = DummyProgress()
            try:
                progress.done()
            except UnboundLocalError:
                pass
        self._redraw()

class StatCanon(glcanon.GLCanon, interpret.StatMixin):
    def __init__(self, colors, geometry, is_foam, lathe_view_option, stat, random, text, linecount, progress, arcdivision):
        glcanon.GLCanon.__init__(self, colors, geometry, is_foam)
        interpret.StatMixin.__init__(self, stat, random)
        self.lathe_view_option = lathe_view_option
        self.text = text
        self.linecount = linecount
        self.progress = progress
        self.aborted = False
        self.arcdivision = arcdivision

    def is_lathe(self): return self.lathe_view_option

    def change_tool(self, pocket):
        glcanon.GLCanon.change_tool(self,pocket)
        interpret.StatMixin.change_tool(self,pocket)

    # not sure if this is used - copied from AXIS code
    def do_cancel(self, event):
        self.aborted = True

    # not sure if this is used - copied from AXIS code
    def check_abort(self):
        #root_window.update()
        if self.aborted: raise KeyboardInterrupt

    def next_line(self, st):
        glcanon.GLCanon.next_line(self, st)
        self.progress.update(self.lineno)
        if self.notify:
            self.output_notify_message(self.notify_message)
            self.notify = 0

    # this is class patched
    # output the text from the magic comment eg: (PREVIEW,notify,The text)
    def output_notify_message(self, message):
        pass