Hi folks.
Earlier messages suggested a nice singleton decorator, which is shown
in the draft PEP:
def singleton(cls):
return cls()
class MyClass [singleton]:
...
This has been mentioned as an argument against requiring or recommending
that decorators accept and return callables.
But i don't think this is a good way to write a singleton, because then
the user of the class has to get instances by saying "MyClass" instead
of "MyClass()". Better would be:
def singleton(cls):
instances = {}
def getinstance():
if cls not in instances:
instances[cls] = cls()
return instances[cls]
return getinstance
Then, code that gets an instance makes more sense. MyClass() still
instantiates MyClass -- it just always returns the same instance.
I respectfully suggest that the PEP use the latter implementation in
its singleton example instead.
-- ?!ng
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