_event_context_manager.py

# Copyright (c) Microsoft Corporation.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

import asyncio
from typing import Any, Coroutine, Generic, Optional, TypeVar, cast

T = TypeVar("T")


class EventInfoImpl(Generic[T]):
    def __init__(self, coroutine: Coroutine) -> None:
        self._value: Optional[T] = None
        self._task = asyncio.get_event_loop().create_task(coroutine)
        self._done = False

    @property
    async def value(self) -> T:
        if not self._done:
            self._value = await self._task
            self._done = True
        return cast(T, self._value)


class EventContextManagerImpl(Generic[T]):
    def __init__(self, coroutine: Coroutine) -> None:
        self._event: EventInfoImpl = EventInfoImpl(coroutine)

    async def __aenter__(self) -> EventInfoImpl[T]:
        return self._event

    async def __aexit__(self, *args: Any) -> None:
        await self._event.value