for testing and deploying your application
for finding and fixing issues
for empowering human code reviews
import typing as t
class Singleton(type):
"""Singleton Design Pattern imlemented as a Metaclass.
Use this Metaclass to design your class (constructor) with the Singleton
Pattern. Setting your class's 'metaclass' key to this Metaclass (see
example below), will restrict object instantiation so that it always return
the same (singleton) object.
Example:
>>> class ObjectDict(metaclass=Singleton):
... def __init__(self):
... self.objects = {}
>>> reg1 = ObjectDict()
>>> reg1.objects['a'] = 1
>>> reg2 = ObjectRegistry()
>>> reg2.objects['b'] = 2
>>> reg3 = ObjectRegistry()
>>> reg2.objects == {'a': 1}
True
>>> reg3.objects['a'] == 1
>>> reg3.objects['b'] == 2
>>> id(reg1) == id(reg2) == id(reg3)
"""
_instances: t.Mapping[t.Type, t.Any] = {}
def __call__(cls: t.Type, *args, **kwargs) -> t.Any:
instance = cls._instances.get(cls)
if not instance:
instance = super(Singleton, cls).__call__(*args, **kwargs)
cls._instances[cls] = instance
return instance
boromir674 /
software-patterns
