singletondecorator.py

this is the most basic to learn python

#: c01:SingletonDecorator.py
class SingletonDecorator:
  def __init__(self,klass):
    self.klass = klass
    self.instance = None
  def __call__(self,*args,**kwds):
    if self.instance == None:
      self.instance = self.klass(*args,**kwds)
    return self.instance

class foo: pass
foo = SingletonDecorator(foo)

x=foo()
y=foo()
z=foo()
x.val = 'sausage'
y.val = 'eggs'
z.val = 'spam'
print x.val
print y.val
print z.val
print x is y is z
#<hr>
output = '''
spam
spam
spam
1
'''