code: def tot_edges(self):
          
          all_edges = []
          for facet in self.facets:
              edges = []
              pt = self.get_line_in_facet(facet)
  
              lines = []
              for i, p in enumerate(pt):
                  if i == len(pt) / 2:
                      break
                  lines.append(tuple(sorted(tuple([tuple(pt[i*2]), tuple(pt[i*2+1])]))))
  
              for i, p in enumerate(lines):
                  if p not in all_edges:
                      edges.append(p)
  
              all_edges.extend(edges)
  
          return len(all_edges)
docs: Returns the number of edges in the convex hull.
              Useful for identifying catalytically active sites.