commit 0c15c4a0cabaed7eaa37ba4103756b1ad0e85df8 Author: Isis Lovecruft <isis@torproject.org> Date: Wed Oct 31 16:30:43 2012 +0000 * Added a Singleton class which can be subclassed, ensuring that there can only ever be one instance of the subclass, to ooni.utils.process * Style-fixing on a couple of assert statements. --- ooni/utils/process.py | 25 ++++++++++++++++++++++--- 1 files changed, 22 insertions(+), 3 deletions(-) diff --git a/ooni/utils/process.py b/ooni/utils/process.py index e9f56a0..25d6368 100644 --- a/ooni/utils/process.py +++ b/ooni/utils/process.py @@ -39,9 +39,9 @@ def singleton_semaphore(deferred_process_init, callback chain has completed. This should be a fully initialized process connected to a :class:`twisted.internet.reactor`. """ - assert type(callbacks) is list - assert type(errbacks) is list - assert type(max_inits) is int + assert isinstance(callbacks, list) + assert isinstance(errbacks, list) + assert isinstance(max_inits, int) for cb in callbacks: deferred_process_init.addCallback(cb) @@ -52,3 +52,22 @@ def singleton_semaphore(deferred_process_init, singleton = yield only_this_many.run(deferred_process_init) defer.returnValue(singleton) +class Singleton(object): + """ + Generic Class for creating Singleton subclasses. + + Subclass me to create a singleton class, which will only ever have one + instance, regardless of how many times the subclass constructor is called. + + Any subclass of me should override ``init`` rather than ``__init__``, + because the latter is called whenever the constructor is called. + """ + def __new__(cls, *args, **kwds): + it = cls.__dict__.get("__it__") + if it is not None: + return it + cls.__it__ = it = object.__new__(cls) + it.init(*args, **kwds) + return it + def init(self, *args, **kwds): + pass