Python 反射含有协程方法类的问题

项目有个需求要动态获取模块内的所有协程方法，查了点资料发现 python 里面反射对象可以使用getattr()和对象内置的__dict__属性两种方式，但是我发现两种方式再处理静态的协程方法时结果不一样：

使用getattr()

a = __import__('a')
print('===========getattr()=============')
func_sync = getattr(a, 'func_sync')
func_async = getattr(a, 'func_async')
print(func_sync)  # <function func_sync at 0x7f827b98f510>
print(func_async)  # <function func_async at 0x7f8279cd01e0>
print(asyncio.iscoroutinefunction(func_async))  # True
# getattr class
A = getattr(a, 'A')
print(A)  # <class 'a.A'>
method_aa = getattr(A, 'aa')
method_bb = getattr(A, 'bb')
method_cc = getattr(A, 'cc')
print(method_aa)  # <bound method A.aa of <class 'a.A'>>  <----这里的 bound method 是什么意思？
print(method_bb)  # <function A.bb at 0x7f8279cd00d0>
print(method_cc)  # <function A.cc at 0x7f8279cd0158>
print(asyncio.iscoroutinefunction(method_aa))  # True  <---- 注意这里
print(asyncio.iscoroutinefunction(method_bb))  # True
print(asyncio.iscoroutinefunction(method_cc))  # False

使用__dict__

print('=========== __dict__ =============')
A = a.__dict__['A']
func_sync = a.__dict__['func_sync']
func_async = a.__dict__['func_async']
print(asyncio.iscoroutinefunction(func_async))  # True
print(A)  # <class 'a.A'>
method_aa = A.__dict__['aa']
method_bb = A.__dict__['bb']
method_cc = A.__dict__['cc']
print(method_aa)  # <classmethod object at 0x7f827a21c908>  <---- 变成了 classmethod
print(method_bb)  # <function A.bb at 0x7f8279cd00d0>
print(method_cc)  # <function A.cc at 0x7f8279cd0158>
print(asyncio.iscoroutinefunction(method_aa))  # False <----- 不应该是 True 吗？
print(asyncio.iscoroutinefunction(method_bb))  # True
print(asyncio.iscoroutinefunction(method_cc))  # False

我感觉__dict__和getattr()在反射对象的机制上应该有一些区别，但是 google 了半天也没搞明白为什么，求指教！

a.py

class A:

    @classmethod
    async def aa(cls):
        return 123

    async def bb(self):
        return 456

    def cc(self):
        return 789


def func_sync():
    return 'sync'


async def func_async():
    return 'async'

wwqgtxx

2018-06-18 13:20:41 +08:00

个人猜测，应该原因在这里：

asyncio.iscoroutinefunction:
return (getattr(func, '_is_coroutine', None) is _is_coroutine or _inspect_iscoroutinefunction(func))

inspect.iscoroutinefunction:
return bool((isfunction(object) or ismethod(object)) andobject.__code__.co_flags & CO_COROUTINE)

通过实验
>>>A.aa
<bound method A.aa of <class 'A'>>
>>>A.__dict__["aa"]
<classmethod object at 0x000002BDE92F7F60>
>>>inspect.ismethod(A.__dict__["aa"])
False
>>>inspect.isfunction(A.__dict__["aa"])
False
>>>inspect.ismethod(A.aa)
True
>>>inspect.isfunction(A.aa)
False

所以你通过 A.__dict__['aa']得到的是一个 classmethod object 而根本就不是一个 method 也不是一个 function，当然他也就不是一个 coroutinefunction 了，至于为什么这么判断，那就得看写这段代码的人是怎么想的了