16.9. AsyncIO Debug

  • By default asyncio runs in production mode

  • Asyncio has a debug mode which can be enabled

  • More verbose message you can achieve by using PYTHONASYNCIODEBUG=1 and PYTHONTRACEMALLOC=1 environment variables

  • Also python3 -X dev -X tracemalloc=5 myfile.py

16.9.1. Debug

  • By default asyncio runs in production mode

  • Asyncio has a debug mode which can be enabled

$ PYTHONMALLOC=debug PYTHONASYNCIODEBUG=1 python3 -X dev -X tracemalloc=5 myfile.py

Asyncio has a debug mode which can be enabled by:

  • Setting the PYTHONASYNCIODEBUG environment variable to 1.

  • Using the Python Development Mode.

  • Passing debug=True to asyncio.run().

  • Calling loop.set_debug().

In addition to enabling the debug mode, consider also:

  • setting the log level of the asyncio logger to logging.basicConfig(level=logging.DEBUG)

  • configuring the warnings module to display ResourceWarning warnings. One way of doing that is by using the -W default command line option.

When the debug mode is enabled:

  • asyncio checks for coroutines that were not awaited and logs them; this mitigates the 'forgotten await' pitfall.

  • Many non-threadsafe asyncio APIs (such as loop.call_soon() and loop.call_at() methods) raise an exception if they are called from a wrong thread.

  • The execution time of the I/O selector is logged if it takes too long to perform an I/O operation.

  • Callbacks taking longer than 100ms are logged.

  • The loop.slow_callback_duration attribute can be used to set the minimum execution duration in seconds that is considered 'slow'.

16.9.2. Introspection

  • asyncio.current_task(loop=None) - Return the currently running Task instance, or None if no task is running.

  • asyncio.all_tasks(loop=None) - Return a set of not yet finished Task objects run by the loop.

  • If loop is None, get_running_loop() is used for getting current loop.

16.9.3. Further Reading