Warning
Policies are deprecated and will be removed in Python 3.16. Users are encouraged to use the
function or the
with loop_factory to use the desired loop implementation.
An event loop policy is a global object used to get and set the current
, as well as create new event loops. The default policy can be
with
to use different event loop implementations, or substituted by a
that can override these behaviors.
The
gets and sets a separate event loop per context. This is per-thread by default, though custom policies could define context differently.
Custom event loop policies can control the behavior of
,
, and
.
Policy objects should implement the APIs defined in the
abstract base class.
Getting and Setting the Policy
The following functions can be used to get and set the policy for the current process:
asyncio.get_event_loop_policy()
Return the current process-wide policy.
Deprecated since version 3.14: The get_event_loop_policy() function is deprecated and will be removed in Python 3.16.
asyncio.set_event_loop_policy(policy)
Set the current process-wide policy to policy.
If policy is set to None, the default policy is restored.
Deprecated since version 3.14: The set_event_loop_policy() function is deprecated and will be removed in Python 3.16.
Policy Objects
The abstract event loop policy base class is defined as follows:
classasyncio.AbstractEventLoopPolicy
An abstract base class for asyncio policies.
get_event_loop()
Get the event loop for the current context.
Return an event loop object implementing the
interface.
This method should never return None.
Changed in version 3.6.
set_event_loop(loop)
Set the event loop for the current context to loop.
new_event_loop()
Create and return a new event loop object.
This method should never return None.
Deprecated since version 3.14: The AbstractEventLoopPolicy class is deprecated and will be removed in Python 3.16.
asyncio ships with the following built-in policies:
classasyncio.DefaultEventLoopPolicy
The default asyncio policy. Uses
on Unix and
on Windows.
There is no need to install the default policy manually. asyncio is configured to use the default policy automatically.
Changed in version 3.8: On Windows,
is now used by default.
Changed in version 3.14: The
method of the default asyncio policy now raises a
if there is no set event loop.
Deprecated since version 3.14: The DefaultEventLoopPolicy class is deprecated and will be removed in Python 3.16.
classasyncio.WindowsSelectorEventLoopPolicy
An alternative event loop policy that uses the
event loop implementation.
Deprecated since version 3.14: The WindowsSelectorEventLoopPolicy class is deprecated and will be removed in Python 3.16.
classasyncio.WindowsProactorEventLoopPolicy
An alternative event loop policy that uses the
event loop implementation.
Deprecated since version 3.14: The WindowsProactorEventLoopPolicy class is deprecated and will be removed in Python 3.16.
Custom Policies
To implement a new event loop policy, it is recommended to subclass
and override the methods for which custom behavior is wanted, e.g.:
classMyEventLoopPolicy(asyncio.DefaultEventLoopPolicy):defget_event_loop(self):"""Get the event loop. This may be None or an instance of EventLoop. """loop=super().get_event_loop()# Do something with loop ...returnloopasyncio.set_event_loop_policy(MyEventLoopPolicy())