Class TransformNode

   object --+    
            |    
Node.VLibNode --+
                |
               TransformNode

Known Subclasses:

NodeLib.SmartsRemover.SmartsRemover

base class for nodes which filter their input

Assumptions:

  - transform function takes a number of arguments equal to the
    number of inputs we have.  We return whatever it returns

  - inputs (parents) can be stepped through in lockstep

Usage Example:
  >>> from VLib.Supply import SupplyNode
  >>> def func(a,b):
  ...   return a+b
  >>> tform = TransformNode(func)
  >>> suppl1 = SupplyNode(contents=[1,2,3,3])
  >>> suppl2 = SupplyNode(contents=[1,2,3,1])
  >>> tform.AddParent(suppl1)
  >>> tform.AddParent(suppl2)
  >>> v = [x for x in tform]
  >>> v
  [2, 4, 6, 4]
  >>> tform.reset()
  >>> v = [x for x in tform]
  >>> v
  [2, 4, 6, 4]

  If we don't provide a function, just return the inputs:
  >>> tform = TransformNode()
  >>> suppl1 = SupplyNode(contents=[1,2,3,3])
  >>> suppl2 = SupplyNode(contents=[1,2,3,1])
  >>> tform.AddParent(suppl1)
  >>> tform.AddParent(suppl2)
  >>> v = [x for x in tform]
  >>> v
  [(1, 1), (2, 2), (3, 3), (3, 1)]

x.__init__(...) initializes x; see x.__class__.__doc__ for signature

part of the iterator interface

raises StopIteration on failure