new_contents: from base64 import b64encode
  
  from . import PiwikQueryReportEventBase
  
  
  class PiwikQueryEventGraphBase(PiwikQueryReportEventBase):
      """Base Piwik query for retrieving PNG graphs"""
  
      def call(self, apiModule, apiAction, height=None, width=None, graphType='verticalBar', **query_params):
          if height is not None:
              query_params['height'] = height
          if width is not None:
              query_params['width'] = width
          return super(PiwikQueryEventGraphBase, self).call(method='ImageGraph.get',
                                                            apiModule=apiModule, apiAction=apiAction,
                                                            aliasedGraph='1', graphType=graphType, **query_params)
  
      def get_result(self):
          """Perform the call and return the graph data
  
          :return: Encoded PNG graph data string to be inserted in a `src`
                   atribute of a HTML img tag.
          """
          img_prefix = 'data:image/png;base64,'
          png = self.call(default_response='none')
          if png == 'none':
              return png
          img_code = b64encode(png)
          return img_prefix + img_code
  
  
  class PiwikQueryEventGraphVisits(PiwikQueryEventGraphBase):
      def call(self, **query_params):
          return super(PiwikQueryEventGraphVisits, self).call(apiModule='VisitsSummary', apiAction='get', width=720,
                                                              height=260, graphType='evolution', **query_params)
  
  
  class PiwikQueryEventGraphDevices(PiwikQueryEventGraphBase):
      def call(self, **query_params):
          return super(PiwikQueryEventGraphDevices, self).call(apiModule='UserSettings', apiAction='getOS',
                                                               period='range', width=320, height=260,
                                                               graphType='horizontalBar', **query_params)
  
  
  class PiwikQueryEventGraphCountries(PiwikQueryEventGraphBase):
      def call(self, **query_params):
          return super(PiwikQueryEventGraphCountries, self).call(apiModule='UserCountry', apiAction='getCountry',
                                                                 period='range', width=490, height=260,
                                                                 graphType='horizontalBar', **query_params)
  
subject: Add graph queries