title: Error when adding edges to network graph: 'v_of_edge' for a cleaned list entry
body: <p>I have a cleaned list.
  Like ['42,1', '42,2', '42,18']
  I skip the rest cause its very long.
  When I try to use add_edge in networkx. It comes up the error</p>
  <pre><code>add_edge() missing 1 required positional argument: 'v_of_edge'
  </code></pre>
  <p>Here is my code.</p>
  <pre><code>for i in cleanedList:
    G.add_edge(i)
  </code></pre>
  <p>I believe i in cleanedList is already as a form 42,1. So I try to directly pass it into add_edge. How could this can be fixed?</p>