code: def append(nodelist, node, label=None, sep='_'):
      
  
      nname = node.__name__
  
      # Determine label
      label = label or len(nodelist)
  
      # Look for separator at the end of name
      ind = nname.rfind(sep)
  
      # If there is no separator, we will remove last character and
      # replace with label.
      node.__name__ = nname[:ind] + sep + str(label)
  
      nodelist.append(node)
  
      return nodelist
docs: Append function to automate the naming of list elements in Containers.
  
      :Arguments:
          - `nodelist` : List containing nodes for Container.
          - `node` : Node to be added to list.
          - `label` : Label to be appended to list (If not passed,
          defaults to element number).
          - `sep` : Separator character for label (defaults to underscore).
  
      :Return:
          - `nodelist` : Passed list with node added.