GraphElement is the Base class for Nodes and Edges.

A GraphElement.data property is provided to give easier
access to all of the element’s non-structural member
variables. It returns a dictionary.

It also provides an __repr __ member function to make
easier work of analyzing your graphs.

__repr__(self):

 Pretty prints this element.

__lt__(self, other):

Arbitrary comparison for sorting.

GraphElement has the following two properties

data(self):

 Returns a dictionary representing the data values of this element.

 Note that elements which are marked private- ie, start with a single  
 underscore- will not appear in this dictionary.

key(self):

 Generates a key suitable for datawise association in a dictionary.

 As with the data attribute, this does not include data values which  
 are prefixed with an underscore.