Added example answers for chapters 13 and 14 to fix #1

CH_13_async_io/exercise_01/solution_00.py

@@ -0,0 +1,76 @@
+# Try to create a `asyncio` base class that automatically
+# registers all instances for easy closing/destructuring when you
+# are done
+import abc
+import asyncio
+
+
+class AsyncBase(abc.ABC):
+    _instances = []
+
+    def __init__(self):
+        self._instances.append(self)
+
+    async def close(self):
+        raise NotImplementedError
+
+
+class AsyncManager(AsyncBase):
+    # Use a separate class for the managing of the instances so
+    # we don't pollute the namespace of the base class
+
+    @classmethod
+    async def close(cls):
+        # Make sure to clear the list of instances while closing
+        while cls._instances:
+            await cls._instances.pop().close()
+
+    # Support `async with` syntax as well
+    async def __aenter__(self):
+        return self
+
+    async def __aexit__(self, exc_type, exc, tb):
+        await self.close()
+
+
+class A(AsyncBase):
+    def __init__(self):
+        super().__init__()
+        print('A.__init__')
+
+    async def close(self):
+        print('A.close')
+
+
+class B(AsyncBase):
+    def __init__(self):
+        super().__init__()
+        print('B.__init__')
+
+    async def close(self):
+        print('B.close')
+
+
+async def main():
+    print('Using close method directly')
+
+    A()
+    B()
+    await AsyncManager.close()
+
+    print()
+
+
+async def main_with():
+    print('Using async with')
+
+    async with AsyncManager():
+        A()
+        B()
+
+    print()
+
+
+if __name__ == '__main__':
+    asyncio.run(main())
+    asyncio.run(main_with())