How to draw a chart with OFC Python?

I need to visualize data for my trac Plugin. Therefore I want to use Open Flash Charts 2. Trying to follow this didn't quite work out as expected.

Question

The Chartdata won't show, the only output is the loading-animation by OFC. Everything looks similar too the html-source in the tutorial.

How can I load the JSON- Data into my chart?

Additional Information

I wrote a template where the processed data should be entered.

CHART_TEMPLATE = Template(
              '''
              <script type=\"text/javascript\" src=\"$json_path/json2.js\">
              </script>
              <script type=\"text/javascript\" src=\"$js_path/swfobject.js\">
              </script>
              <script type=\"text/javascript\">
              swfobject.embedSWF(\"$ofc_path/open-flash-chart.swf\", 
\"$chartname\", \"$width\", \"$height\", \"9.0.0\");

              function open_flash_chart_data()
              {
              alert('reading data');
              return JSON.stringify($json_chart_data);
              }

              function ofc_ready()
              {
              alert('ofc_ready');
              }
              </script>

              <div id=\"$chartname\"></div>
              '''
              )

The data is transformed to JSON with Open Flash Charts python, which seems to work well.

def chartdata_from_timetable(self, dict, title):
    '''
    creates chartdata in JSON-format from 2 dim dictionary

    '''
    elements = []
    x_labels = []
    dc = DateConversion.DateConversion()
    # if startdate on a weekend, startdate might 
    not be inluced in the dict->    
    choose next monday
    for key in timetable[startdate]:
        element = Chart()
        element.type = "line"
        element.text = key
        values = []
        for date in dict:
            values.append(dict[date][key])
            x_labels.append(string_from_date(date))
        element.values = values
        elements.append(element)
    chart = Chart()
    chart.x_axis.labels = x_labels
    chart.title.text = title
    chart.elements = elements
    return chart.create().encode()

Afterwards the following data is returned, none seems to be missing:

CHART_TEMPLATE.safe_substitute(js_path = config['js_dir'],...,
json_chart_data = chart_data)

You have to check if the path of the ofc folder in trac.ini is right.
The function chartdata_from_timetable is also not right. You only see the values of the last entry because of overwriting.