Design-Patterns-in-Python/singleton.py at master · coder-zh/Design-Patterns-in-Python · GitHub

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# ---------- Singletone ----------

# Real Singleton instance

class Singleton(object):

def __new__(type):

if not '_the_instance' in type.__dict__:

type._the_instance = object.__new__(type)

return type._the_instance

a = Singleton()

a.toto = 12

b = Singleton()

print b.toto

print id(a), id(b) # The same !!

# ---------- Borg's singletone ----------

class Borg:

__shared_state = {}

def __init__(self):

self.__dict__ = self.__shared_state

a = Borg()

a.toto = 12

b = Borg()

print b.toto

print id(a), id(b) # different ! but states are sames

# ---------- Alex's Martelli examples ----------

class Singleton(object):

def __new__(cls, *a, **k):

if not hasattr(cls, '_inst'):

cls._inst = super(Singleton, cls

).__new__(cls, *a, **k)

return cls._inst

class Borg(object):

"""Subclassing is no problem."""

_shared_state = {}

def __new__(cls, *a, **k):

obj = super(Borg, cls).__new__(cls, *a, **k)

obj.__dict__ = cls._shared_state

return obj

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