On 02/28/2015 09:29 PM, y...@zioup.com wrote: >> Problem 4: >> You speak of a singleton. But you haven't implemented one. It is not >> clear from your code if this class should be a singleton. I'm guessing >> not. Singletons are in fact rare. Well, let me put it another way: >> Good reasons to code a singleton are rare. > > Thanks. I hadn't realise "singleton" meant a class built such that it could > not be instanciated more than once, I thought it corresponded to a pattern > where only one object is ever created from a given class.
Is not "only one object is ever created from a given class" the same as "could not be [instantiated] more than once?" To be clear, singletons are commonly used in Python every time you import a module. A module *is* a singleton pattern, particularly one that maintains state. I use sometimes use this feature for sharing config and other data between other modules (global state when it's required). "import module" essentially does the one-time instantiation if it's a new import; top-level code in the module is run once on first import, where it acts like a constructor. So it functions as a singleton. As near as I can tell there's very little reason to make a class-based singleton in Python, since a module has the same effect and is cleaner. -- https://mail.python.org/mailman/listinfo/python-list
