::: currentmodule asyncio ::: # Runners **Source code:** `Lib/asyncio/runners.py`{.interpreted-text role="source"} This section outlines high-level asyncio primitives to run asyncio code. They are built on top of an `event loop `{.interpreted-text role="ref"} with the aim to simplify async code usage for common wide-spread scenarios. ::: {.contents depth="1" local=""} ::: ## Running an asyncio Program :::::::::: function run(coro, \*, debug=None, loop_factory=None) Execute *coro* in an asyncio event loop and return the result. The argument can be any awaitable object. This function runs the awaitable, taking care of managing the asyncio event loop, *finalizing asynchronous generators*, and closing the executor. This function cannot be called when another asyncio event loop is running in the same thread. If *debug* is `True`, the event loop will be run in debug mode. `False` disables debug mode explicitly. `None` is used to respect the global `asyncio-debug-mode`{.interpreted-text role="ref"} settings. If *loop_factory* is not `None`, it is used to create a new event loop; otherwise `asyncio.new_event_loop`{.interpreted-text role="func"} is used. The loop is closed at the end. This function should be used as a main entry point for asyncio programs, and should ideally only be called once. It is recommended to use *loop_factory* to configure the event loop instead of policies. Passing `asyncio.EventLoop`{.interpreted-text role="class"} allows running asyncio without the policy system. The executor is given a timeout duration of 5 minutes to shutdown. If the executor hasn\'t finished within that duration, a warning is emitted and the executor is closed. Example: async def main(): await asyncio.sleep(1) print('hello') asyncio.run(main()) ::: versionadded 3.7 ::: ::: versionchanged 3.9 Updated to use `loop.shutdown_default_executor`{.interpreted-text role="meth"}. ::: ::: versionchanged 3.10 *debug* is `None` by default to respect the global debug mode settings. ::: ::: versionchanged 3.12 Added *loop_factory* parameter. ::: ::: versionchanged 3.14 *coro* can be any awaitable object. ::: :::: note ::: title Note ::: The `!asyncio`{.interpreted-text role="mod"} policy system is deprecated and will be removed in Python 3.16; from there on, an explicit *loop_factory* is needed to configure the event loop. :::: :::::::::: ## Runner context manager :::::::::: {.Runner(*, .debug=None, .loop_factory=None)} A context manager that simplifies *multiple* async function calls in the same context. Sometimes several top-level async functions should be called in the same `event loop `{.interpreted-text role="ref"} and `contextvars.Context`{.interpreted-text role="class"}. If *debug* is `True`, the event loop will be run in debug mode. `False` disables debug mode explicitly. `None` is used to respect the global `asyncio-debug-mode`{.interpreted-text role="ref"} settings. *loop_factory* could be used for overriding the loop creation. It is the responsibility of the *loop_factory* to set the created loop as the current one. By default `asyncio.new_event_loop`{.interpreted-text role="func"} is used and set as current event loop with `asyncio.set_event_loop`{.interpreted-text role="func"} if *loop_factory* is `None`. Basically, `asyncio.run`{.interpreted-text role="func"} example can be rewritten with the runner usage: async def main(): await asyncio.sleep(1) print('hello') with asyncio.Runner() as runner: runner.run(main()) ::: versionadded 3.11 ::: :::: method run(coro, \*, context=None) Execute *coro* in the embedded event loop. The argument can be any awaitable object. If the argument is a coroutine, it is wrapped in a Task. An optional keyword-only *context* argument allows specifying a custom `contextvars.Context`{.interpreted-text role="class"} for the code to run in. The runner\'s default context is used if context is `None`. Returns the awaitable\'s result or raises an exception. This function cannot be called when another asyncio event loop is running in the same thread. ::: versionchanged 3.14 *coro* can be any awaitable object. ::: :::: ::: method close() Close the runner. Finalize asynchronous generators, shutdown default executor, close the event loop and release embedded `contextvars.Context`{.interpreted-text role="class"}. ::: ::: method get_loop() Return the event loop associated with the runner instance. ::: :::: note ::: title Note ::: `Runner`{.interpreted-text role="class"} uses the lazy initialization strategy, its constructor doesn\'t initialize underlying low-level structures. Embedded *loop* and *context* are created at the `with`{.interpreted-text role="keyword"} body entering or the first call of `run`{.interpreted-text role="meth"} or `get_loop`{.interpreted-text role="meth"}. :::: :::::::::: ## Handling Keyboard Interruption ::: versionadded 3.11 ::: When `signal.SIGINT`{.interpreted-text role="const"} is raised by `Ctrl-C`{.interpreted-text role="kbd"}, `KeyboardInterrupt`{.interpreted-text role="exc"} exception is raised in the main thread by default. However this doesn\'t work with `asyncio`{.interpreted-text role="mod"} because it can interrupt asyncio internals and can hang the program from exiting. To mitigate this issue, `asyncio`{.interpreted-text role="mod"} handles `signal.SIGINT`{.interpreted-text role="const"} as follows: 1. `asyncio.Runner.run`{.interpreted-text role="meth"} installs a custom `signal.SIGINT`{.interpreted-text role="const"} handler before any user code is executed and removes it when exiting from the function. 2. The `~asyncio.Runner`{.interpreted-text role="class"} creates the main task for the passed coroutine for its execution. 3. When `signal.SIGINT`{.interpreted-text role="const"} is raised by `Ctrl-C`{.interpreted-text role="kbd"}, the custom signal handler cancels the main task by calling `asyncio.Task.cancel`{.interpreted-text role="meth"} which raises `asyncio.CancelledError`{.interpreted-text role="exc"} inside the main task. This causes the Python stack to unwind, `try/except` and `try/finally` blocks can be used for resource cleanup. After the main task is cancelled, `asyncio.Runner.run`{.interpreted-text role="meth"} raises `KeyboardInterrupt`{.interpreted-text role="exc"}. 4. A user could write a tight loop which cannot be interrupted by `asyncio.Task.cancel`{.interpreted-text role="meth"}, in which case the second following `Ctrl-C`{.interpreted-text role="kbd"} immediately raises the `KeyboardInterrupt`{.interpreted-text role="exc"} without cancelling the main task.