# asyncio-runner
asyncio
# Runners **Source code:** `Lib/asyncio/runners.py` This section outlines high-level asyncio primitives to run asyncio code. They are built on top of an `event loop ` with the aim to simplify async code usage for common wide-spread scenarios.
## Running an asyncio Program
run(coro, \*, debug=None, loop_factory=None, eager_tasks=False) 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` settings. If *loop_factory* is not `None`, it is used to create a new event loop; otherwise `asyncio.new_event_loop` 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. If *eager_tasks* is `True`, the created loop is configured to use `eager-task-factory` by default. 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. > [!NOTE] > Users concerned about performance are encouraged to experiment with `eager_tasks=True` in their code. Example: async def main(): await asyncio.sleep(1) print('hello') asyncio.run(main())
3.7
3.9 Updated to use `loop.shutdown_default_executor`.
3.10 *debug* is `None` by default to respect the global debug mode settings.
3.12 Added *loop_factory* parameter.
3.14 *coro* can be any awaitable object.
3.16 Added *eager_tasks* parameter.
## Runner context manager
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 ` and `contextvars.Context`. 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` 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` is used and set as current event loop with `asyncio.set_event_loop` if *loop_factory* is `None`. If *eager_tasks* is `True`, the created loop is configured to use `eager-task-factory` by default. Basically, `asyncio.run` 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()) > [!NOTE] > Users concerned about performance are encouraged to experiment with `eager_tasks=True` in their code.
3.11
3.16 Added *eager_tasks* parameter.
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` 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.
3.14 *coro* can be any awaitable object.
close() Close the runner. Finalize asynchronous generators, shutdown default executor, close the event loop and release embedded `contextvars.Context`.
get_loop() Return the event loop associated with the runner instance.
> [!NOTE] > `Runner` uses the lazy initialization strategy, its constructor doesn't initialize underlying low-level structures. > > Embedded *loop* and *context* are created at the `with` body entering or the first call of `run` or `get_loop`.
## Handling Keyboard Interruption
3.11
When `signal.SIGINT` is raised by `Ctrl-C`, `KeyboardInterrupt` exception is raised in the main thread by default. However this doesn't work with `asyncio` because it can interrupt asyncio internals and can hang the program from exiting. To mitigate this issue, `asyncio` handles `signal.SIGINT` as follows: 1. `asyncio.Runner.run` installs a custom `signal.SIGINT` handler before any user code is executed and removes it when exiting from the function. 2. The `~asyncio.Runner` creates the main task for the passed coroutine for its execution. 3. When `signal.SIGINT` is raised by `Ctrl-C`, the custom signal handler cancels the main task by calling `asyncio.Task.cancel` which raises `asyncio.CancelledError` 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` raises `KeyboardInterrupt`. 4. A user could write a tight loop which cannot be interrupted by `asyncio.Task.cancel`, in which case the second following `Ctrl-C` immediately raises the `KeyboardInterrupt` without cancelling the main task.