title: NetworkX directed graph, no weights and self arc
body: <p>I would like a self-loop from node 1 to itself. I tried <code>G.add_edge(1,1)</code> but that did not work. My code is as follows</p>
  
  <pre><code>import networkx as nx
  import pylab
  
  G = nx.DiGraph()
  
  G.add_node(1,pos=(1,1))
  
  G.add_node(2,pos=(0,0))
  G.add_node(3,pos=(2,0))
  G.add_edge(1,2)
  G.add_edge(1,3)
  G.add_edge(1,1)
  
  
  pos=nx.get_node_attributes(G,'pos')
  nx.draw(G,pos)
  
  pylab.show()
  </code></pre>