singleton-decorator1 0.5.5

Singleton decorator which is: thread-safe, copy safe, mypy compliant, not wrapped class

###Singleton Decorator Library

A decorator based on wiki.python.org Python Decorators Library, namely https://wiki.python.org/moin/PythonDecoratorLibrary#Singleton, with significant improvements.

Features (assuming you decorate a class definition of MyClass)

• Every call of MyClass() results in the same instance, which persists from the first instantiation until the end of execution
• Even if you delete all your references to the instance, it still persists to be returned on the next call of MyClass()
• That instance is only initiallized once (the first time)
• is_instance(MyClass(), MyClass) is True (that is, we do not wrap the class)
• Using copy() or deepcopy() simply gives another reference to the single instance
• The overhead of locking in the threaded version is low enough that you may use it even before adding threading to your class.
• If MyClass is threadsafe, then annotating with @threaded_singleton will give a threadsafe singleton (only the safety of creating the first instance requires locking, as all other singleton actions are no-ops or simply return a reference to the single instance)
• If MyClass has locking (either Lock or RLock) in the initialization (new and init) the singleton locking does not deadlock.
• The test suite is included, so you can tell if I verified correctly
• The singleton decorator and test bench pass black and mypy
• The test suite is automatically run before publishing

This has some fixes (correct calling of old init, correct replacement of init, removal of copy and deepcopy), plus a threadsafe version

from singleton_decorator1 import singleton
@singleton
class MyClass...

or

from singleton_decorator1 import threaded_singleton
@threaded_singleton
class MyThreadsafeClass...

Note that if MyThreadsafeClass is not threadsafe, then the decorator will not fix that -- it only ensures that the singleton functionality is thread safe.

The library can be built with poetry >= 2.0:
[Recommended]
if needed, install pyenv
pyenv install 3.10
pyenv local 3.10

[required]
(pip show poetry | grep -q "Version: 2") || pip install --ignore installed poetry==2

poetry env use $(pyenv which python) or
poetry env use $(which python)

poetry install

poetry build