v2.0.3 (2020-11-27)

  • Mark eventlet and gevent support as deprecated. The support will be removed in Pykka 3.0.

    These where somewhat interesting ways to implement concurrency in Python when Pykka was conceived in 2011. Today, it is unclear it these libraries still have any mindshare or if keeping the support for them just adds an unecessary burden to Pykka’s maintenance.

  • Include Python 3.9 in the test matrix. (PR: #98)

  • Add missing None default value for the timeout keyword argument to wait(), so that it matches the Event API. (PR: #91)

v2.0.2 (2019-12-02)

Bugfix release.

  • Fix test suite run with pytest-mocker >= 1.11.2. (Fixes: #85)

v2.0.1 (2019-10-10)

Bugfix release.

v2.0.0 (2019-05-07)

Major feature release.


  • Drop support for Python 2.6, 3.2, 3.3, and 3.4. All have reached their end of life and do no longer receive security updates.
  • Include CPython 3.5, 3.6, 3.7, and 3.8 pre-releases, and PyPy 3.5 in the test matrix.
  • Include gevent and Eventlet tests in all environments. Since Pykka was originally developed, both has grown support for Python 3 and PyPy.
  • On Python 3, import Callable and Iterable from instead of collections. This fixes a deprecation warning on Python 3.7 and prepares for Python 3.8.


  • Actor messages are no longer required to be dict objects. Any object type can be used as an actor message. (Fixes: #39, #45, PR: #79)

    For existing code, this means that on_receive() implementations should no longer assume the received message to be a dict, and guard with the appropriate amount of isinstance() checks. As an existing application will not observe any new message types before it starts using them itself, this is not marked as backwards incompatible.


  • Backwards incompatible: Avoid accessing actor properties when creating a proxy for the actor. For properties with side effects, this is a major bug fix. For properties which does heavy work, this is a major startup performance improvement.

    This is backwards incompatible if you in a property getter returned an object instance with the pykka_traversable marker. Previously, this would work just like a traversable attribute. Now, the property always returns a future with the property getter’s return value.

  • Fix infinite recursion when creating a proxy for an actor with an attribute or method replaced with a Mock without a spec defined. (Fixes: #26, #27)

  • Fix infinite recursion when creating a proxy for an actor with an attribute that was itself a proxy to the same actor. The attribute will now be ignored and a warning log message will ask you to consider making the self-proxy private. (Fixes: #48)

  • Add defer() to support method calls through a proxy with tell() semantics. (Contributed by Andrey Gubarev. Fixes: #63. PR: #72)

  • Add traversable() for marking an actor’s attributes as traversable when used through actor proxies. The old way of manually adding a pykka_traversable attribute to the object to be traversed still works, but the new function is recommended as it provides protection against typos in the marker name, and keeps the traversable marking in the actor class itself. (PR: #81)


  • Backwards incompatible: pykka.Future.set_exception() no longer accepts an exception instance, which was deprecated in 0.15. The method can be called with either an exc_info tuple or None, in which case it will use sys.exc_info() to get information on the current exception.

  • Backwards incompatible: on a future with an iterable result no longer applies the map function to each item in iterable. Instead, the entire future result is passed to the map function. (Fixes: #64)

    To upgrade existing code, make sure to explicitly apply the core of your map function to each item in the iterable:

    >>> f = pykka.ThreadingFuture()
    >>> f.set([1, 2, 3])
    >>> x: x + 1).get()  # Pykka < 2.0
    [2, 3, 4]
    >>> x: [i + 1 for i in x]).get()  # Pykka >= 2.0
    [2, 3, 4]

    This change makes it easy to use map() to extract a field from a future that returns a dict:

    >>> f = pykka.ThreadingFuture()
    >>> f.set({'foo': 'bar'})
    >>> x: x['foo']).get()

    Because dict is an iterable, the now removed special handling of iterables made this pattern difficult to use.

  • Reuse result from pykka.Future.filter(),, and pykka.Future.reduce(). Recalculating the result on each call to pykka.Future.get() is both inconsistent with regular futures and can cause problems if the function is expensive or has side effects. (Fixes: #32)

  • If using Python 3.5+, one can now use the await keyword to get the result from a future. (Contributed by Joshua Doncaster-Marsiglio. PR: #78)


  • Pykka’s use of different log levels has been documented.
  • Exceptions raised by an actor that are captured into a reply future are now logged on the INFO level instead of the DEBUG level. This makes it possible to detect potentially unhandled exceptions during development without having to turn on debug logging, which can have a low signal to noise ratio. (Contributed by Stefan Möhl. Fixes: #73)

Gevent support

  • Ensure that the original traceback is preserved when an exception is returned through a future from a Gevent actor. (Contributed by Arne Brutschy. Fixes: #74, PR: #75)


  • Backwards incompatible: Prefix all internal modules with _. This is backwards incompatible if you have imported objects from other import paths than what is used in the documentation.
  • Port tests to pytest.
  • Format code with Black.
  • Change internal messaging format from dict to namedtuple. (PR: #80)

v1.2.1 (2015-07-20)

  • Increase log level of pykka.debug.log_thread_tracebacks() debugging helper from logging.INFO to logging.CRITICAL.
  • Fix errors in docs examples. (PR: #29, #43)
  • Fix typos in docs.
  • Various project setup and development improvements.

v1.2.0 (2013-07-15)

  • Enforce that multiple calls to pykka.Future.set() raises an exception. This was already the case for some implementations. The exception raised is not specified.

  • Add pykka.Future.set_get_hook().

  • Add filter(), join(), map(), and reduce() as convenience methods using the new set_get_hook() method.

  • Add support for running actors based on eventlet greenlets. See pykka.eventlet for details. Thanks to Jakub Stasiak for the implementation.

  • Update documentation to reflect that the reply_to field on the message is private to Pykka. Actors should reply to messages simply by returning the response from on_receive(). The internal field is renamed to pykka_reply_to a to avoid collisions with other message fields. It is also removed from the message before the message is passed to on_receive(). Thanks to Jakub Stasiak.

  • When messages are left in the actor inbox after the actor is stopped, those messages that are expecting a reply is now rejected by replying with an ActorDeadError exception. This causes other actors blocking on the returned Future without a timeout to raise the exception instead of waiting forever. Thanks to Jakub Stasiak.

    This makes the behavior of messaging an actor around the time it is stopped more consistent:

    • Messaging an already dead actor immediately raises ActorDeadError.
    • Messaging an alive actor that is stopped before it processes the message will cause the reply future to raise ActorDeadError.

    Similarly, if you ask an actor to stop multiple times, and block on the responses, all the messages will now get an reply. Previously only the first message got a reply, potentially making the application wait forever on replies to the subsequent stop messages.

  • When ask() is used to asynchronously message a dead actor (e.g. block set to False), it will no longer immediately raise ActorDeadError. Instead, it will return a future and fail the future with the ActorDeadError exception. This makes the interface more consistent, as you’ll have one instead of two ways the call can raise exceptions under normal conditions. If ask() is called synchronously (e.g. block set to True), the behavior is unchanged.

  • A change to stop() reduces the likelyhood of a race condition when asking an actor to stop multiple times by not checking if the actor is dead before asking it to stop, but instead just go ahead and leave it to tell() to do the alive-or-dead check a single time, and as late as possible.

  • Change is_alive() to check the actor’s runnable flag instead of checking if the actor is registered in the actor registry.

v1.1.0 (2013-01-19)

v1.0.1 (2012-12-12)

  • Name the threads of pykka.ThreadingActor after the actor class name instead of “PykkaThreadingActor-N” to ease debugging. (Fixes: #12)

v1.0.0 (2012-10-26)

  • Backwards incompatible: Removed pykka.VERSION and pykka.get_version(), which have been deprecated since v0.14. Use pykka.__version__ instead.

  • Backwards incompatible: Removed pykka.ActorRef.send_one_way() and pykka.ActorRef.send_request_reply(), which have been deprecated since v0.14. Use pykka.ActorRef.tell() and pykka.ActorRef.ask() instead.

  • Backwards incompatible: Actors no longer subclass threading.Thread or gevent.Greenlet. Instead they have a thread or greenlet that executes the actor’s main loop.

    This is backwards incompatible because you no longer have access to fields/methods of the thread/greenlet that runs the actor through fields/methods on the actor itself. This was never advertised in Pykka’s docs or examples, but the fields/methods have always been available.

    As a positive side effect, this fixes an issue on Python 3.x, that was introduced in Pykka 0.16, where pykka.ThreadingActor would accidentally override the method threading.Thread._stop().

  • Backwards incompatible: Actors that override __init__() must call the method they override. If not, the actor will no longer be properly initialized. Valid ways to call the overridden __init__() method include:

    # or
    # or
  • Make pykka.Actor.__init__() accept any arguments and keyword arguments by default. This allows you to use super() in __init__() like this:

    super().__init__(1, 2, 3, foo='bar')

    Without this fix, the above use of super() would cause an exception because the default implementation of __init__() in pykka.Actor would not accept the arguments.

  • Allow all public classes and functions to be imported directly from the pykka module. E.g. from import ThreadingActor can now be written as from pykka import ThreadingActor. The exception is pykka.gevent, which still needs to be imported from its own package due to its additional dependency on gevent.

v0.16 (2012-09-19)

  • Let actors access themselves through a proxy. See the pykka.ActorProxy documentation for use cases and usage examples. (Fixes: #9)
  • Give proxies direct access to the actor instances for inspecting available attributes. This access is only used for reading, and works since both threading and gevent based actors share memory with other actors. This reduces the creation cost for proxies, which is mostly visible in test suites that are starting and stopping lots of actors. For the Mopidy test suite the run time was reduced by about 33%. This change also makes self-proxying possible.
  • Fix bug where pykka.Actor.stop() called by an actor on itself did not process the remaining messages in the inbox before the actor stopped. The behavior now matches the documentation.

v0.15 (2012-08-11)

  • Change the argument of pykka.Future.set_exception() from an exception instance to a exc_info three-tuple. Passing just an exception instance to the method still works, but it is deprecated and may be unsupported in a future release.
  • Due to the above change, pykka.Future.get() will now reraise exceptions with complete traceback from the point when the exception was first raised, and not just a traceback from when it was reraised by get(). (Fixes: #10)

v0.14 (2012-04-22)

  • Add pykka.__version__ to conform with PEP 396. This deprecates pykka.VERSION and pykka.get_version().
  • Add pykka.ActorRef.tell() method in favor of now deprecated pykka.ActorRef.send_one_way().
  • Add pykka.ActorRef.ask() method in favor of now deprecated pykka.ActorRef.send_request_reply().
  • ThreadingFuture.set() no longer makes a copy of the object set on the future. The setter is urged to either only pass immutable objects through futures or copy the object himself before setting it on the future. This is a less safe default, but it removes unecessary overhead in speed and memory usage for users of immutable data structures. For example, the Mopidy test suite of about 1000 tests, many which are using Pykka, is still passing after this change, but the test suite runs approximately 20% faster.

v0.13 (2011-09-24)

  • 10x speedup of traversable attribute access by reusing proxies.
  • 1.1x speedup of callable attribute access by reusing proxies.

v0.12.4 (2011-07-30)

  • Change and document order in which pykka.ActorRegistry.stop_all() stops actors. The new order is the reverse of the order the actors were started in. This should make stop_all work for programs with simple dependency graphs in between the actors. For applications with more complex dependency graphs, the developer still needs to pay attention to the shutdown sequence. (Fixes: #8)

v0.12.3 (2011-06-25)

  • If an actor that was stopped from pykka.Actor.on_start(), it would unregister properly, but start the receive loop and forever block on receiving incoming messages that would never arrive. This left the thread alive and isolated, ultimately blocking clean shutdown of the program. The fix ensures that the receive loop is never executed if the actor is stopped before the receive loop is started.
  • Set the thread name of any pykka.ThreadingActor to PykkaActorThread-N instead of the default Thread-N. This eases debugging by clearly labeling actor threads in e.g. the output of threading.enumerate().
  • Add utility method pykka.ActorRegistry.broadcast() which broadcasts a message to all registered actors or to a given class of registred actors. (Fixes: #7)
  • Allow multiple calls to pykka.ActorRegistry.unregister() with the same as argument without throwing a ValueError. (Fixes: #5)
  • Make the pykka.ActorProxy’s reference to its pykka.ActorRef public as pykka.ActorProxy.actor_ref. The ActorRef instance was already exposed as a public field by the actor itself using the same name, but making it public directly on the proxy makes it possible to do e.g. proxy.actor_ref.is_alive() without waiting for a potentially dead actor to return an ActorRef instance you can use. (Fixes: #3)

v0.12.2 (2011-05-05)

  • Actors are now registered in pykka.registry.ActorRegistry before they are started. This fixes a race condition where an actor tried to stop and unregister itself before it was registered, causing an exception in ActorRegistry.unregister().

v0.12.1 (2011-04-25)

v0.12 (2011-03-30)

  • First stable release, as Pykka now is used by the Mopidy project. From now on, a changelog will be maintained and we will strive for backwards compatibility.