James Stroud wrote:
> Nathan Harmston wrote:
>> And also preventing more than one Manager instance instantiated at one
>> time.
>
> Forgot to answer this. You want the singleton pattern:
>
> http://aspn.activestate.com/ASPN/Cookbook/Python/Recipe/52558
But not really a singleton now that I think about it...
class Singletonish(object):
""" A python singletonish """
class __impl(object):
""" Implementation of the singletonish interface """
def spam(self):
""" Test method, return singletonish id """
return id(self)
# storage for the instance reference
__instance = None
def __init__(self):
""" Create singletonish instance """
Singletonish.__instance = Singletonish.__impl()
def __getattr__(self, attr):
""" Delegate access to implementation """
if attr == '__id__':
return id(Singletonish.__instance)
return getattr(Singletonish.__instance, attr)
def __setattr__(self, attr, value):
""" Delegate access to implementation """
return setattr(Singletonish.__instance, attr, value)
In action:
py> class Singletonish(object):
... """ A python singletonish """
... class __impl(object):
... """ Implementation of the singletonish interface """
... def spam(self):
... """ Test method, return singletonish id """
... return id(self)
... # storage for the instance reference
... __instance = None
... def __init__(self):
... """ Create singletonish instance """
... Singletonish.__instance = Singletonish.__impl()
... def __getattr__(self, attr):
... """ Delegate access to implementation """
... return getattr(Singletonish.__instance, attr)
... def __setattr__(self, attr, value):
... """ Delegate access to implementation """
... return setattr(Singletonish.__instance, attr, value)
...
py> s = Singletonish()
py> print s.spam()
18727248
py>
py> t = Singletonish()
py> print t.spam()
18682480
py> print s.spam()
18682480
Of course t and s are not /really/ the same:
py> print id(t)
18727056
py> print id(s)
18727280
py> assert t is s
------------------------------------------------------------
Traceback (most recent call last):
File "<ipython console>", line 1, in <module>
<type 'exceptions.AssertionError'>
But this shouldn't matter unless you have a special use case because the
implementation to all Singletonish objects are delegated to to the
latest __impl object and so behave identically.
James
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