title: Making dynamic graphs in python's Networkx
body: <p>I am trying to make a dynamic graph using networkx. For example when I use:</p>
  
  <pre><code>import networkx as nx
  G = nx.Graph()
  </code></pre>
  
  <p>it makes an empty graph G which is by default static. How can I change it to dynamic? Some nodes/edges may exist in one timestamp but not in the others. How can I incorporate time?
  As an example, suppose my graph has three nodes 'a', 'b' and 'c'. At time t1, there is only one edge between 'a' and 'b'. At time t2 the configuration of edges changes and in this timestamp all nodes are connected to each other. Say:</p>
  
  <pre><code>G.add_edge('a','b',timestamp='t1')
  G.add_node('c',timestamp='t1')
  
  G.add_edge('a','b',timestamp='t2')
  G.add_edge('a','c',timestamp='t2')
  G.add_edge('b','c',timestamp='t2')
  </code></pre>
  
  <p>but this does not work! </p>
  
  <p>the reason I need to do this is that I want to save the graph in gexf format to use it in Gephi.</p>
  
  <p>What should I do?</p>