docs: def dbg_draw(self, filename):
          """
          Draw the graph and save it to a PNG file.
          """
          import matplotlib.pyplot as pyplot  # pylint: disable=import-error
          from networkx.drawing.nx_agraph import graphviz_layout  # pylint: disable=import-error
  
          tmp_graph = networkx.DiGraph()
          for from_block, to_block in self.transition_graph.edges():
              node_a = "%#08x" % from_block.addr
              node_b = "%#08x" % to_block.addr
              if node_b in self._ret_sites:
                  node_b += "[Ret]"
              if node_a in self._call_sites:
                  node_a += "[Call]"
              tmp_graph.add_edge(node_a, node_b)
          pos = graphviz_layout(tmp_graph, prog='fdp')   # pylint: disable=no-member
          networkx.draw(tmp_graph, pos, node_size=1200)
          pyplot.savefig(filename)