'''singleton.py: A Python implementation of the Singleton pattern.

  Do not edit this file.  It is extracted automatically from the
  documentation:
    http://www.nmt.edu/tcc/help/lang/python/examples/logscan/
'''

# - - - - -   c l a s s   S i n g l e t o n

class Singleton(object):
    '''Base class for singleton objects.

      State/Invariants:
        Singleton.__classMap:
          [ a dictionary whose keys are the classes
            instantiated so far, and each related value
            is the single instance of that class ]
    '''
    __classMap = {}
# - - -   S i n g l e t o n . _ _ n e w _ _

    def __new__ ( cls, *args, **kw ):
        '''Instance factory.

          [ if cls is a key in Singleton.__classMap ->
              return the related value
            else ->
              Singleton.__classMap[cls]  :=  a new
                  object of class cls
              return that new object ]
        '''
        #-- 1 --
        try:
            return Singleton.__classMap[cls]
        except KeyError:
            inst = Singleton.__classMap[cls] = object.__new__(cls)
            return inst