title: Bulbs: How to check if two vertices are connected by an edge in Titan
body: <p>I am using TitanGraphDB + Cassandra.I am starting Titan as follows</p>
  
  <pre><code>cd titan-cassandra-0.3.1
  bin/titan.sh config/titan-server-rexster.xml config/titan-server-cassandra.properties
  </code></pre>
  
  <p>I have a Rexster shell that I can use to communicate to Titan+Cassandra above.</p>
  
  <pre><code>cd rexster-console-2.3.0
  bin/rexster-console.sh
  </code></pre>
  
  <p>I am attempting to model a network topology using Titan Graph DB.I want to program the Titan Graph DB from my python program.I am using bulbs package for that.
  I create three types of vertices </p>
  
  <pre><code> - switch
   - port 
   - device
  </code></pre>
  
  <p>I create labelled edges between ports that are connected physically.The label that I use is  "link".</p>
  
  <p>Let us say I have two port vertices <code>portA</code> and <code>portB</code>.</p>
  
  <p>I want to write a function as below</p>
  
  <pre><code>def is_connected(portA, portB):
       ...
       ... 
       ...
  </code></pre>
  
  <p>How do I find if two vertices are "connected by a labelled edge"? </p>
  
  <p>I have two graph vertices </p>
  
  <pre><code>src_sw_other_ports
  &lt;Vertex: http://localhost:8182/graphs/graph/vertices/48&gt;
  
  dst_sw_other_ports
  &lt;Vertex: http://localhost:8182/graphs/graph/vertices/72&gt;
  </code></pre>
  
  <p>I have tried </p>
  
  <pre><code>link_exists = src_sw_other_ports.out.retain([dst_sw_other_ports]).hasNext()
  </code></pre>
  
  <p>It is giving me the following error.</p>
  
  <pre><code>  File "/home/karthik/Projects/ryu/ryu/app/simple_switch.py", line 238, in compute_path
      link_exists = src_sw_other_ports.out.retain([dst_sw_other_ports]).hasNext()
    File "/usr/local/lib/python2.7/dist-packages/bulbs/element.py", line 209, in __getattr__
      raise AttributeError(name)
  AttributeError: out
  </code></pre>