code: def fmt_part(part, node_labels=None):
      
      def nodes(x):  # pylint: disable=missing-docstring
          return ','.join(labels(x, node_labels)) if x else EMPTY_SET
  
      numer = nodes(part.mechanism)
      denom = nodes(part.purview)
  
      width = max(3, len(numer), len(denom))
      divider = HORIZONTAL_BAR * width
  
      return (
          '{numer:^{width}}\n'
          '{divider}\n'
          '{denom:^{width}}'
      ).format(numer=numer, divider=divider, denom=denom, width=width)
docs: Format a |Part|.
  
      The returned string looks like::
  
          0,1
          ───
           ∅