docs: def show_flow(self):
          '''
          API: relabel(self, i)
          Description:
          Used by max_flow_preflowpush() method for display purposed.
          Post:
              'color' and 'label' attribute of edges/nodes are updated.
          '''
          for n in self.get_node_list():
              excess = self.get_node_attr(n, 'excess')
              distance = self.get_node_attr(n, 'distance')
              self.set_node_attr(n, 'label', str(excess)+'/'+str(distance))
              for neighbor in self.get_neighbors(n):
                  capacity = self.get_edge_attr(n, neighbor, 'capacity')
                  flow = self.get_edge_attr(n, neighbor, 'flow')
                  if capacity == INF:
                      self.set_edge_attr(n, neighbor, 'label',
                                         'INF'+'/'+str(flow))
                  else:
                      self.set_edge_attr(n, neighbor, 'label',
                                         str(capacity)+'/'+str(flow))
                  if capacity == flow:
                      self.set_edge_attr(n, neighbor, 'color', 'red')
                  elif flow > 0:
                      self.set_edge_attr(n, neighbor, 'color', 'green')
                  else:
                      self.set_edge_attr(n, neighbor, 'color', 'black')
          self.display()