code: def get_part(self, vertex_in, vertices_border):
          
          vertices_new = set(self.neighbors[vertex_in])
          vertices_part = set([vertex_in])
  
          while len(vertices_new) > 0:
              pivot = vertices_new.pop()
              if pivot in vertices_border:
                  continue
              vertices_part.add(pivot)
              pivot_neighbors = set(self.neighbors[pivot])
              pivot_neighbors -= vertices_part
              vertices_new |= pivot_neighbors
  
          return vertices_part
docs: List all vertices that are connected to vertex_in, but are not
             included in or 'behind' vertices_border.