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# Copyright (C) 2006-2007 Dan Pascu. See LICENSE for details.
#
"""Miscelaneous utility functions and classes"""
__all__ = ['Singleton', 'Null']
class Singleton(type):
"""Metaclass for making singletons"""
def __init__(cls, name, bases, dic):
super(Singleton, cls).__init__(name, bases, dic)
cls.instance = None
def __call__(cls, *args, **kw):
if cls.instance is None:
cls.instance = super(Singleton, cls).__call__(*args, **kw)
return cls.instance
class Null(object):
"""Instances of this class always and reliably "do nothing"."""
def __init__(self, *args, **kwargs): pass
def __call__(self, *args, **kwargs): return self
def __repr__(self): return self.__class__.__name__
def __nonzero__(self): return 0
def __eq__(self, other): return isinstance(other, self.__class__)
def __ne__(self, other): return not isinstance(other, self.__class__)
def __getattr__(self, name): return self
def __setattr__(self, name, value): return self
def __delattr__(self, name): return self
__str__ = __repr__
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