code: def get_html(self, chart_obj=None, slug=None):
          
          if chart_obj is None:
              if self.chart_obj is None:
                  self.err(
                      "No chart object registered, please provide "
                      "one in parameters"
                  )
                  return
              chart_obj = self.chart_obj
          try:
              if self.engine == "bokeh":
                  html = self._get_bokeh_html(chart_obj)
                  if html is None:
                      self.err("No html returned for " + str(chart_obj))
                  return html
              elif self.engine == "altair":
                  html = self._get_altair_html_(chart_obj, slug)
                  if html is None:
                      self.err("No html returned for " + str(chart_obj))
                  return html
              else:
                  self.err("Chart engine " + self.engine + " unknown")
                  return
          except Exception as e:
              self.err(e, "Can not get html from chart object")
docs: Get the html and script tag for a chart