# Proxies

class pykka.ActorProxy(actor_ref, attr_path=None)

  An `ActorProxy` wraps an `ActorRef` instance. The proxy allows the referenced actor to be used through regular method calls and field access.

  You can create an `ActorProxy` from any `ActorRef`:

      actor_ref = MyActor.start()
      actor_proxy = ActorProxy(actor_ref)

  You can also get an `ActorProxy` by using `proxy()`:

      actor_proxy = MyActor.start().proxy()

  Attributes and method calls

  When reading an attribute or getting a return value from a method, you get a `Future` object back. To get the enclosed value from the future, you must call `get()` on the returned future:

      print(actor_proxy.string_attribute.get())
      print(actor_proxy.count().get() + 1)

  If you call a method just for it’s side effects and do not care about the return value, you do not need to accept the returned future or call `get()` on the future. Simply call the method, and it will be executed concurrently with your own code:

      actor_proxy.method_with_side_effect()

  If you want to block your own code from continuing while the other method is processing, you can use `get()` to block until it completes:

      actor_proxy.method_with_side_effect().get()

  If you’re using Python 3.5+, you can also use the `await` keyword to block until the method completes:

      await actor_proxy.method_with_side_effect()

  If you access a proxied method as an attribute, without calling it, you get an `CallableProxy`.

  Proxy to itself

  An actor can use a proxy to itself to schedule work for itself. The scheduled work will only be done after the current message and all messages already in the inbox are processed.

  For example, if an actor can split a time consuming task into multiple parts, and after completing each part can ask itself to start on the next part using proxied calls or messages to itself, it can react faster to other incoming messages as they will be interleaved with the parts of the time consuming task. This is especially useful for being able to stop the actor in the middle of a time consuming task.

  To create a proxy to yourself, use the actor’s `actor_ref` attribute:

      proxy_to_myself_in_the_future = self.actor_ref.proxy()

  If you create a proxy in your actor’s constructor or `on_start` method, you can create a nice API for deferring work to yourself in the future:

      def __init__(self):
          ...
          self._in_future = self.actor_ref.proxy()
          ...

      def do_work(self):
          ...
          self._in_future.do_more_work()
          ...

      def do_more_work(self):
          ...

  To avoid infinite loops during proxy introspection, proxies to self should be kept as private instance attributes by prefixing the attribute name with `_`.

  Examples

  An example of `ActorProxy` usage:

      #!/usr/bin/env python3

      import pykka

      class Adder(pykka.ThreadingActor):
          def add_one(self, i):
              print(f'{self} is increasing {i}')
              return i + 1

      class Bookkeeper(pykka.ThreadingActor):
          def __init__(self, adder):
              super().__init__()
              self.adder = adder

          def count_to(self, target):
              i = 0
              while i < target:
                  i = self.adder.add_one(i).get()
                  print(f'{self} got {i} back')

      if __name__ == '__main__':
          adder = Adder.start().proxy()
          bookkeeper = Bookkeeper.start(adder).proxy()
          bookkeeper.count_to(10).get()
          pykka.ActorRegistry.stop_all()

  Parameters

    actor_ref (`pykka.ActorRef`) – reference to the actor to proxy

  Raise

    `pykka.ActorDeadError` if actor is not available

  actor_ref = None

    The actor’s `pykka.ActorRef` instance.

class pykka.CallableProxy(actor_ref, attr_path)

  Proxy to a single method.

  `CallableProxy` instances are returned when accessing methods on a `ActorProxy` without calling them.

  Example:

      proxy = AnActor.start().proxy()

      # Ask semantics returns a future. See `__call__()` docs.
      future = proxy.do_work()

      # Tell semantics are fire and forget. See `defer()` docs.
      proxy.do_work.defer()

  __call__(*args, **kwargs)

    Call with `ask()` semantics.

    Returns a future which will yield the called method’s return value.

    If the call raises an exception is set on the future, and will be reraised by `get()`. If the future is left unused, the exception will not be reraised. Either way, the exception will also be logged. See Logging for details.

  defer(*args, **kwargs)

    Call with `tell()` semantics.

    Does not create or return a future.

    If the call raises an exception, there is no future to set the exception on. Thus, the actor’s `on_failure()` hook is called instead.

    New in version 2.0.

pykka.traversable(obj)

  Marks an actor attribute as traversable.

  The traversable marker makes the actor attribute’s own methods and attributes available to users of the actor through an `ActorProxy`.

  Used as a function to mark a single attribute:

      class AnActor(pykka.ThreadingActor):
          playback = pykka.traversable(Playback())

      class Playback(object):
          def play(self):
              return True

  This function can also be used as a class decorator, making all instances of the class traversable:

      class AnActor(pykka.ThreadingActor):
          playback = Playback()

      @pykka.traversable
      class Playback(object):
          def play(self):
              return True

  The third alternative, and the only way in Pykka < 2.0, is to manually mark a class as traversable by setting the `pykka_traversable` attribute to `True`:

      class AnActor(pykka.ThreadingActor):
          playback = Playback()

      class Playback(object):
          pykka_traversable = True

          def play(self):
              return True

  When the attribute is marked as traversable, its methods can be executed in the context of the actor through an actor proxy:

      proxy = AnActor.start().proxy()
      assert proxy.playback.play().get() is True

  New in version 2.0.