Python - 装饰器装饰class，访问闭包中的自由变量

Posted 2020-11-27 allen2333

def singleton(cls):
    instances = {}
    def wrapper(*args, **kwargs):
        if cls not in instances:
            instances[cls] = cls(*args, **kwargs)
        return instances[cls]
    return wrapper
    
@singleton
class Foo:
    pass

f1 = Foo()
f2 = Foo()
print(dir(Foo))

# (<cell at 0x7f9ad3ede040: type object at 0x55929df326a0>, <cell at 0x7f9ad3e9e580: dict object at 0x7f9ad3ee8140>)
print(Foo.__closure__)  
print(Foo.__closure__[1].cell_contents) # {<class ‘__main__.Foo‘>: <__main__.Foo object at 0x7f1533a19be0>}