code: def create_label(label_tuple, extra_label=None):
      
      if extra_label is not None:
          return '[' + ' - '.join(label_tuple) + '] ' + str(extra_label)
      else:
          return '[' + ' - '.join(label_tuple) + ']'
docs: Return a label based on my_tuple (a,b) and extra label.
  
      a and b are string.
  
      The output will be something like:
                  [a - b] extra_label