asyncio
源代码： Lib/asyncio/futures.py , Lib/asyncio/base_futures.py
Future 对象用于桥接 基于回调的低级代码 采用高级 async/await 代码。
返回 True if obj 是：
True
实例化的 asyncio.Future ,
asyncio.Future
实例化的 asyncio.Task ,
asyncio.Task
像 Future 对象具有 _asyncio_future_blocking 属性。
_asyncio_future_blocking
Added in version 3.5.
返回：
obj argument as is, if obj 是 Future ， Task , or a Future-like object ( isfuture() is used for the test.)
Future
Task
isfuture()
a Task object wrapping obj ，若 obj is a coroutine ( iscoroutine() is used for the test); in this case the coroutine will be scheduled by ensure_future() .
iscoroutine()
ensure_future()
a Task object that would await on obj ，若 obj is an awaitable ( inspect.isawaitable() is used for the test.)
inspect.isawaitable()
若 obj is neither of the above a TypeError 被引发。
TypeError
重要
另请参阅 create_task() function which is the preferred way for creating new Tasks.
create_task()
Save a reference to the result of this function, to avoid a task disappearing mid-execution.
3.5.1 版改变： The function accepts any awaitable 对象。
从 3.10 版起弃用： Deprecation warning is emitted if obj is not a Future-like object and loop is not specified and there is no running event loop.
包裹 concurrent.futures.Future 对象在 asyncio.Future 对象。
concurrent.futures.Future
从 3.10 版起弃用： Deprecation warning is emitted if future is not a Future-like object and loop is not specified and there is no running event loop.
A Future represents an eventual result of an asynchronous operation. Not thread-safe.
Future 是 awaitable object. Coroutines can await on Future objects until they either have a result or an exception set, or until they are cancelled. A Future can be awaited multiple times and the result is same.
Typically Futures are used to enable low-level callback-based code (e.g. in protocols implemented using asyncio 传输 ) to interoperate with high-level async/await code.
The rule of thumb is to never expose Future objects in user-facing APIs, and the recommended way to create a Future object is to call loop.create_future() . This way alternative event loop implementations can inject their own optimized implementations of a Future object.
loop.create_future()
3.7 版改变： 添加支持 contextvars 模块。
contextvars
从 3.10 版起弃用： Deprecation warning is emitted if loop is not specified and there is no running event loop.
返回 Future 的结果。
若 Future 是 done and has a result set by the set_result() method, the result value is returned.
set_result()
若 Future 是 done and has an exception set by the set_exception() method, this method raises the exception.
set_exception()
If the Future has been cancelled , this method raises a CancelledError 异常。
CancelledError
If the Future’s result isn’t yet available, this method raises a InvalidStateError 异常。
InvalidStateError
Mark the Future as done and set its result.
引发 InvalidStateError error if the Future is already done .
Mark the Future as done and set an exception.
返回 True 若 Future 是 done .
A Future is done if it was cancelled or if it has a result or an exception set with set_result() or set_exception() 调用。
返回 True 若 Future cancelled .
The method is usually used to check if a Future is not cancelled before setting a result or an exception for it:
if not fut.cancelled(): fut.set_result(42)
Add a callback to be run when the Future is done .
The callback is called with the Future object as its only argument.
If the Future is already done when this method is called, the callback is scheduled with loop.call_soon() .
loop.call_soon()
可选仅关键词 context 自变量允许指定自定义 contextvars.Context 为 callback to run in. The current context is used when no context 被提供。
contextvars.Context
functools.partial() can be used to pass parameters to the callback, e.g.:
functools.partial()
# Call 'print("Future:", fut)' when "fut" is done. fut.add_done_callback( functools.partial(print, "Future:"))
3.7 版改变： The context keyword-only parameter was added. See PEP 567 了解更多细节。
移除 callback 从回调列表。
Returns the number of callbacks removed, which is typically 1, unless a callback was added more than once.
取消 Future 并调度回调。
If the Future is already done or cancelled ，返回 False . Otherwise, change the Future’s state to cancelled , schedule the callbacks, and return True .
False
3.9 版改变： 添加 msg 参数。
Return the exception that was set on this Future.
The exception (or None if no exception was set) is returned only if the Future is done .
None
If the Future isn’t done yet, this method raises an InvalidStateError 异常。
Return the event loop the Future object is bound to.
Added in version 3.7.
This example creates a Future object, creates and schedules an asynchronous Task to set result for the Future, and waits until the Future has a result:
async def set_after(fut, delay, value): # Sleep for *delay* seconds. await asyncio.sleep(delay) # Set *value* as a result of *fut* Future. fut.set_result(value) async def main(): # Get the current event loop. loop = asyncio.get_running_loop() # Create a new Future object. fut = loop.create_future() # Run "set_after()" coroutine in a parallel Task. # We are using the low-level "loop.create_task()" API here because # we already have a reference to the event loop at hand. # Otherwise we could have just used "asyncio.create_task()". loop.create_task( set_after(fut, 1, '... world')) print('hello ...') # Wait until *fut* has a result (1 second) and print it. print(await fut) asyncio.run(main())
The Future object was designed to mimic concurrent.futures.Future . Key differences include:
不像 asyncio 未来， concurrent.futures.Future 实例无法等待。
asyncio.Future.result() and asyncio.Future.exception() do not accept the timeout 自变量。
asyncio.Future.result()
asyncio.Future.exception()
asyncio.Future.result() and asyncio.Future.exception() raise an InvalidStateError exception when the Future is not done .
Callbacks registered with asyncio.Future.add_done_callback() are not called immediately. They are scheduled with loop.call_soon() 代替。
asyncio.Future.add_done_callback()
asyncio Future is not compatible with the concurrent.futures.wait() and concurrent.futures.as_completed() 函数。
concurrent.futures.wait()
concurrent.futures.as_completed()
asyncio.Future.cancel() accepts an optional msg argument, but concurrent.futures.Future.cancel() 不会。
asyncio.Future.cancel()
msg
concurrent.futures.Future.cancel()
事件循环
传输和协议
键入搜索术语或模块、类、函数名称。