title: Can't format datetime using Bokeh Hovertool with Custom HTML
body: <p>Using Bokeh to display charts within Flask my hovertools works except for dates, which are my x axis in all charts.  I have tried a hundred permutations of the code and extensively reviewed the documentation and related questions but am missing some key element on how to use formatters within custom html.  This question seems to address my exact question, but I do not see how the answer relates to the actual custom html:
  <a href="https://stackoverflow.com/questions/35128934/bokeh-hover-tool-format-date-variable-in-custom-html">bokeh hover tool - format date variable in custom html</a></p>
  
  <p>The data is passed to bokeh as a pandas data frame then use ColumnDataSource within Bokeh.  The index, and x values, are definitely datetime with Bokeh treating them as a datetime in other parts of the charting such as the x axis labels and ticks.</p>
  
  <p>This is my current hovertools html within Python:</p>
  
  <pre><code>def create_hover_absolute():
  """Generates the HTML for the Bokeh's hover data tool on our graph."""
  hover_html = """
      &lt;div class="plot-tooltip"&gt;
          &lt;div&gt;
              &lt;span style="font-weight: bold;"&gt;$name&lt;/span&gt;
          &lt;/div&gt;
          &lt;div&gt;
              $y{$,000}
          &lt;/div&gt;
          &lt;div&gt;
              Date: @date{%Y-%m}
          &lt;/div&gt;
  
      &lt;/div&gt;
  """
  return HoverTool(tooltips=hover_html, formatters={'date': 'datetime'})
  </code></pre>
  
  <p>I have tried a variety of ways to enter the date including:</p>
  
  <pre><code>$x
  $x with all sorts of formatting such as {%Y%b}
  @date
  @ date with all sorts of formatting
  </code></pre>
  
  <p>I end up with the date as either a long integer (15 digits) or a mysterious three digit number with TIB.  Like this:</p>
  
  <p><a href="https://i.stack.imgur.com/HX9Iq.png" rel="nofollow noreferrer">screenshot showing hover with Date: 118TB%</a></p>
  
  <p>I can make all of this work on the local Bokeh server when I do show(plot) but not in the custom html when passing to web page.  How do I format the date within the html?  How do I include the formatters?</p>
  
  <p>thank you</p>