title: Draw node shape and node color by attribute using networkx
body: <p>In a Graph <code>G</code> i have a set of nodes. Some of them have a Attribute <code>Type</code> which can be <code>MASTER</code> or  <code>DOC</code>. Others do not have the a Type define:</p>
  <pre><code>&gt;&gt;&gt; import networkx as nx
  &gt;&gt;&gt; import matplotlib.pyplot as plt
  &gt;&gt;&gt; G=nx.Graph()
  [...]
  &gt;&gt;&gt; G.node['ART1']
  {'Type': 'MASTER'}
  &gt;&gt;&gt; G.node['ZG1']
  {'Type': 'DOC'}
  &gt;&gt;&gt; G.node['MG1']
  {}
  </code></pre>
  <p>Afterwards I plot the Graph using</p>
  <pre><code>&gt;&gt;&gt; nx.draw(G,with_labels = True)
  &gt;&gt;&gt; plt.show()
  </code></pre>
  <p>Now i get a graph with red Circles. How can I get e.g.
  blue cylces for ART
  red squares for DOC
  purple cylces for everything undefined
  in my plot?</p>