Add solutions

CH_13_async_io/exercise_01/solution_01.py

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+import asyncio
+
+
+class AsyncMeta(type):
+
+    def __new__(mcs, name, bases, namespace):
+        cls = type.__new__(mcs, name, bases, namespace)
+        cls._instances = []
+        origin_new = cls.__new__
+
+        def __new__(cls, *args, **kwargs):
+            ins = origin_new(cls, *args, **kwargs)
+            cls._instances.append(ins)
+            return ins
+
+        cls.__new__ = __new__
+        return cls
+
+    async def close_all(cls):
+        while cls._instances:
+            await cls._instances.pop().close()
+
+    async def __aenter__(cls):
+        return cls
+
+    async def __aexit__(cls, exc_type, exc_val, exc_tb):
+        await cls.close_all()
+
+    def __del__(cls):
+        asyncio.run(cls.close_all())
+
+
+class AsyncClass(metaclass=AsyncMeta):
+
+    def __init__(self):
+        self.name = None
+
+    async def init(self, name):
+        self.name = name
+        print(f'init {name}')
+
+    @classmethod
+    async def create(cls, name):
+        ins = cls()
+        await ins.init(name)
+        return ins
+
+    async def close(self):
+        print(f'close {self.name}')
+
+
+async def main():
+    global AsyncClass
+    print('Using close method directly')
+    egg = await AsyncClass.create('egg')
+    spam = await AsyncClass.create('spam')
+    await AsyncClass.close_all()
+
+    print()
+
+    print('Using async with')
+    async with AsyncClass:
+        egg = await AsyncClass.create('egg')
+        spam = await AsyncClass.create('spam')
+
+    print()
+
+    print('Using __del__')
+    egg = await AsyncClass.create('egg')
+    spam = await AsyncClass.create('spam')
+    # del AsyncClass
+
+
+if __name__ == '__main__':
+    asyncio.run(main())