original_docstring: 
          Return a matrix for a particular trace/field at a subset of the nodes.
          
docstring: Return a matrix for a particular trace/field at a subset of the nodes.
docstring_tokens: Return a matrix for a particular trace / field at a subset of the nodes .
code: def extract(self, trace, t=[], nodes=[]):
          """
          Return a matrix for a particular trace/field at a subset of the nodes.
          """
          raise NotImplementedError
code_tokens: def extract ( self , trace , t = [ ] , nodes = [ ] ) : raise NotImplementedError
short_docstring: Return a matrix for a particular trace/field at a subset of the nodes.
short_docstring_tokens: Return a matrix for a particular trace / field at a subset of the nodes .
comment: """
          Return a matrix for a particular trace/field at a subset of the nodes.
          """