PyPot: base class used by potential terms written in Python.

to write a potential term in Python, define a class which derives from
pyPot.PyPot, and make sure to call the base class' constructor.
Then, the new class should define two methods: 
calcEnergy, and calcEnergyAndDerivs(DerivList). 

Here is a trivial example:

from pyPot import PyPot

class ConstEnergy(PyPot):
  def __init__(s,instanceName,constVal):
      PyPot.__init__(s,instanceName,s)
      s.val = constVal
      return
  def calcEnergy(s):
      return s.val
  def calcEnergyAndDerivs(s,derivs):
      return s.val