Example for immutable inheritance and an example for __new__().

immutable_inheritence.py

class IntWrapper(int):
  ''' int wrapper class. Example for use of __new__().'''

  _valmod5 = None

  def __new__(cls, value):
    ''' Do something to differentiate from int.'''
    self = int.__new__(cls, value) # create an immutable
    return self

  def valmod5(self):
    _valmod5 = self % 5
    return _valmod5

  def self_value(self):
    ''' Actual instance.'''
    return self

if __name__ == '__main__':
  a = IntWrapper(256)
  print a.self_value(), a.valmod5() # 'print a' works the same as 'a.self_value()'