title: Error encounter TypeError: can only concatenate tuple (not "list") to tuple
body: <p>Im following a tutorial on a program to visualize facebook connections and I keep getting "TypeError: can only concatenate tuple (not "list") to tuple" and I don't know how to fix this issue</p>
  
  <pre><code>colors = cl.scales['12']['qual']['Paired']
  def scatter_nodes(pos, labels=None, color='rgb(152, 0, 0)', size=8, opacity=1):
  
      trace = Scatter(x=[], 
                      y=[],  
                      mode='markers', 
                      marker=Marker(
          showscale=False,
          colorscale='Greens',
          reversescale=True,
          color=[], 
          size=10,
      line=dict(width=0)))
      for nd in nodeID:
          trace['x'].append(pos[nd][0])
          trace['y'].append(pos[nd][1])
          color = colors[part[nd] % len(colors)]
          trace['marker']['color'].append(color)
      attrib=dict(name='', text=labels , hoverinfo='text', opacity=opacity) # a dict of Plotly node attributes
      trace=dict(trace, **attrib)# concatenate the dict trace and attrib
      trace['marker']['size']=size
  
      return trace 
  
  def scatter_edges(G, pos, line_color='#a3a3c2', line_width=1, opacity=.2):
      trace = Scatter(x=[], 
                      y=[], 
                      mode='lines'
                     )
      for edge in G.edges():
          trace['x'] += [pos[edge[0]][0],pos[edge[1]][0], None]
          trace['y'] += [pos[edge[0]][1],pos[edge[1]][1], None]  
          trace['hoverinfo']='none'
          trace['line']['width']=line_width
          if line_color is not None: # when it is None a default Plotly color is used
              trace['line']['color']=line_color
      return trace          
  
  labels = []
  
  for nd in nodeID:
        labels.append('{} ({})'.format(nd, part[nd],))
  
  trace1 = scatter_edges(G, pos, line_width=0.25)
  trace2 = scatter_nodes(pos, labels=labels)
  </code></pre>
  
  <p>I tried changing it to parenthesis but that didn't work either. </p>
  
  <p>Error Statement</p>
  
  <pre><code> TypeError                                 Traceback (most recent call last)
  &lt;ipython-input-26-7db6d16fa847&gt; in &lt;module&gt;
  ----&gt; 1 trace1 = scatter_edges(G, pos, line_width=0.25)
        2 trace2 = scatter_nodes(pos, labels=labels)
  
  &lt;ipython-input-23-0e8ff4c52f3c&gt; in scatter_edges(G, pos, line_color, line_width, opacity)
        5                    )
        6     for edge in G.edges():
  ----&gt; 7         trace['x'] += [pos[edge[0]][0],pos[edge[1]][0], None]
        8         trace['y'] += [pos[edge[0]][1],pos[edge[1]][1], None]
        9         trace['hoverinfo']='none'
  
  TypeError: can only concatenate tuple (not "list") to tuple
  </code></pre>