Políticas

Aviso

Policies are deprecated and will be removed in Python 3.16. Users are encouraged to use the asyncio.run() function or the asyncio.Runner with loop_factory to use the desired loop implementation.

An event loop policy is a global object used to get and set the current event loop, as well as create new event loops. The default policy can be replaced with built-in alternatives to use different event loop implementations, or substituted by a custom policy that can override these behaviors.

The policy object 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 get_event_loop(), set_event_loop(), and new_event_loop().

Policy objects should implement the APIs defined in the AbstractEventLoopPolicy 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()

Retorna a política de todo o processo atual.

Obsoleto desde a versão 3.14.0a3 (unreleased): 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.

Obsoleto desde a versão 3.14.0a3 (unreleased): 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:

class asyncio.AbstractEventLoopPolicy

An abstract base class for asyncio policies.

get_event_loop()

Obtém o laço de eventos para o contexto atual.

Return an event loop object implementing the AbstractEventLoop interface.

This method should never return None.

Alterado na versão 3.6.

set_event_loop(loop)

Define o laço de eventos do contexto atual como loop.

new_event_loop()

Cria e retorna um novo objeto de laço de eventos.

This method should never return None.

Obsoleto desde a versão 3.14.0a3 (unreleased): The AbstractEventLoopPolicy class is deprecated and will be removed in Python 3.16.

asyncio ships with the following built-in policies:

class asyncio.DefaultEventLoopPolicy

The default asyncio policy. Uses SelectorEventLoop on Unix and ProactorEventLoop on Windows.

There is no need to install the default policy manually. asyncio is configured to use the default policy automatically.

Alterado na versão 3.8: On Windows, ProactorEventLoop is now used by default.

Alterado na versão 3.14: The get_event_loop() method of the default asyncio policy now raises a RuntimeError if there is no set event loop.

Obsoleto desde a versão 3.14.0a3 (unreleased): The DefaultEventLoopPolicy class is deprecated and will be removed in Python 3.16.

class asyncio.WindowsSelectorEventLoopPolicy

An alternative event loop policy that uses the SelectorEventLoop event loop implementation.

Availability: Windows.

Obsoleto desde a versão 3.14.0a3 (unreleased): The WindowsSelectorEventLoopPolicy class is deprecated and will be removed in Python 3.16.

class asyncio.WindowsProactorEventLoopPolicy

An alternative event loop policy that uses the ProactorEventLoop event loop implementation.

Availability: Windows.

Obsoleto desde a versão 3.14.0a3 (unreleased): 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 DefaultEventLoopPolicy and override the methods for which custom behavior is wanted, e.g.:

class MyEventLoopPolicy(asyncio.DefaultEventLoopPolicy):

    def get_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 ...
        return loop

asyncio.set_event_loop_policy(MyEventLoopPolicy())