def _graphviz(self, dot=None):
from graphviz import Graph, Digraph<EOL>node = self._graph()<EOL>dot = dot or Digraph(comment=self.expression)<EOL>def walk(node):<EOL><INDENT>if isinstance(node, six.string_types):<EOL><INDENT>dot.node(node, node)<EOL>return node, node<EOL><DEDENT>else:<EOL><INDENT>node_repr, fname, fobj, deps = node<EOL>node_id = node_repr<EOL>dot.node(node_id, node_repr)<EOL>for dep in deps:<EOL><INDENT>dep_id, dep = walk(dep)<EOL>dot.edge(node_id, dep_id)<EOL><DEDENT>return node_id, node<EOL><DEDENT><DEDENT>walk(node)<EOL>return dot<EOL>
Return a graphviz.Digraph object with a graph of the expression