flyweight_with_metaclass.py

importweakref


classFlyweightMeta(type):
def__new__(mcs, name, parents, dct):
"""
 Set up object pool

 :param name: class name
 :param parents: class parents
 :param dct: dict: includes class attributes, class methods,
 static methods, etc
 :return: new class
 """
dct["pool"] =weakref.WeakValueDictionary()
returnsuper().__new__(mcs, name, parents, dct)

@staticmethod
def_serialize_params(cls, *args, **kwargs):
"""
 Serialize input parameters to a key.
 Simple implementation is just to serialize it as a string
 """
args_list=list(map(str, args))
args_list.extend([str(kwargs), cls.__name__])
key="".join(args_list)
returnkey

def__call__(cls, *args, **kwargs):
key=FlyweightMeta._serialize_params(cls, *args, **kwargs)
pool=getattr(cls, "pool", {})

instance=pool.get(key)
ifinstanceisNone:
instance=super().__call__(*args, **kwargs)
pool[key] =instance
returninstance


classCard2(metaclass=FlyweightMeta):
def__init__(self, *args, **kwargs):
# print('Init {}: {}'.format(self.__class__, (args, kwargs)))
pass


if__name__=="__main__":
instances_pool=getattr(Card2, "pool")
cm1=Card2("10", "h", a=1)
cm2=Card2("10", "h", a=1)
cm3=Card2("10", "h", a=2)

assert (cm1==cm2) and (cm1!=cm3)
assert (cm1iscm2) and (cm1isnotcm3)
assertlen(instances_pool) ==2

delcm1
assertlen(instances_pool) ==2

delcm2
assertlen(instances_pool) ==1

delcm3
assertlen(instances_pool) ==0