title: Plotly: How to add elements to hover_data using plotly.express piechart?
body: <p>I am playing with examples from plotly.express <a href="https://plot.ly/python/pie-charts/" rel="nofollow noreferrer">piechart help page</a> and trying to add an extra element <code>iso_num</code> to the hover_data property (<code>iso_num</code> is an int64 column in the gapminder dataframe)</p>
  
  <pre><code>import plotly.express as px
  df = px.data.gapminder().query("year == 2007").query("continent == 'Americas'")
  fig = px.pie(df, values='pop', names='country',
               title='Population of American continent',
               hover_data=['lifeExp','iso_num'], labels={'lifeExp':'life expectancy','iso_num':'iso num'
                                                        })
  fig.update_traces(textposition='inside', textinfo='percent+label')
  fig.show()
  </code></pre>
  
  <p>Hovering over the slice of the pie chart then gives this:</p>
  
  <p><a href="https://i.stack.imgur.com/j6PGM.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/j6PGM.png" alt="enter image description here"></a></p>
  
  <p>where <code>iso num</code> value is <code>%{customdata[1]}</code> instead of the numeric value from the column.  </p>
  
  <p>What am I missing?</p>
  
  <p>Thanks!</p>