I'm just trying to streamline one of my classes and have introduced some functionality in the same style as the flyweight design pattern.
However, I'm a bit confused as to why
_dict = dict()
if 'key' in A._dict:
return super(A, cls).__new__(cls)
A._dict['key'] = self
a1 = A()
a2 = A()
a3 = A()
Use __new__ when you need to control the creation of a new instance. Use __init__ when you need to control initialization of a new instance.
__new__ is the first step of instance creation. It's called first, and is responsible for returning a new instance of your class. In contrast, __init__ doesn't return anything; it's only responsible for initializing the instance after it's been created.
In general, you shouldn't need to override __new__ unless you're subclassing an immutable type like str, int, unicode or tuple.
You should consider that what you are trying to do is usually done with a Factory and that's the best way to do it. Using __new__ is not a good clean solution so please consider the usage of a factory. Here you have a good factory example.