How can I require that an abstract base class implement a specific method as a coroutine. For example, consider this ABC:
import abc
class Foo(abc.ABC):
@abc.abstractmethod
async def func():
pass
Now when I subclass and instantiate that:
class Bar(Foo):
def func():
pass
b = Bar()
This succeeds, although func
is not async
, as in the ABC. What can I do so that this only succeeds if func
is async
?
You may use __new__
and check if and how a child class has override parent's coros.
import asyncio
import abc
import inspect
class A:
def __new__(cls, *arg, **kwargs):
# get all coros of A
parent_coros = inspect.getmembers(A, predicate=inspect.iscoroutinefunction)
# check if parent's coros are still coros in a child
for coro in parent_coros:
child_method = getattr(cls, coro[0])
if not inspect.iscoroutinefunction(child_method):
raise RuntimeError('The method %s must be a coroutine' % (child_method,))
return super(A, cls).__new__(cls, *arg, **kwargs)
@abc.abstractmethod
async def my_func(self):
pass
class B(A):
async def my_func(self):
await asyncio.sleep(1)
print('bb')
class C(A):
def my_func(self):
print('cc')
async def main():
b = B()
await b.my_func()
c = C() # this will trigger the RuntimeError
await c.my_func()
loop = asyncio.get_event_loop()
loop.run_until_complete(main())
__new__
as well to suppress this constraint not only async
may be awaited. For example
async def _change_in_db(self, key, value): # some db logic pass def change(self, key, value): if self.is_validate(value): raise Exception('Value is not valid') return self._change_in_db(key, value)
it's ok to call change
like
await o.change(key, value)
Not to mention __await__
in objects, other raw Futures, Tasks...
The technical post webpages of this site follow the CC BY-SA 4.0 protocol. If you need to reprint, please indicate the site URL or the original address.Any question please contact:yoyou2525@163.com.