What’s New



  • Python 3.6 support.


  • Made test suite pass again with latest Hypothesis release.



  • Eliot tasks can now more easily span multiple threads using the new eliot.preserve_context API.
  • eliot-prettyprint command line tool now pretty prints field values in a more informative manner.

Bug fixes:

  • eliot-prettyprint now handles unparseable lines by skipping formatting them rather than exiting.


Bug fixes:

  • Fixed regression in 0.10.0: fix validation of failed actions and tracebacks with extracted additional fields.



Bug fixes:

  • Journald support works on Python 3.



  • Native journald support.
  • eliot-prettyprint is a command-line tool that formats JSON Eliot messages into a more human-friendly format.
  • eliot.logwriter.ThreadedWriter is a Twisted non-blocking wrapper for any blocking destination.



  • Message.log will log a new message, combining the existing Message.new and Message.write.
  • write_traceback and writeFailure no longer require a Logger; they now default to using the global one.
  • The logs written with redirectLogsForTrial are now written in JSON format, rather than with pformat.

Bug fixes:

  • FileDestination will now call flush() on the given file object after writing the log message. Previously log messages would not end up being written out until the file buffer filled up.
  • Each Message logged outside the context of an action now gets a unique task_id.


  • Creating your own Logger instances is no longer necessary; all relevant APIs now default to using a global one. A new testing decorator (eliot.testing.capture_logging) was added to capture global logging.
  • Support positional Field-instance arguments to fields() to make combining existing field types and simple fields more convenient. Contributed by Jonathan Jacobs.
  • write_traceback and writeFailure no longer require a system argument, as the combination of traceback and action context should suffice to discover the origin of the problem. This is a minor change to output format as the field is also omitted from the resulting eliot:traceback messages.
  • The validate_logging testing utility now skips validation when the decorated test method raises SkipTest.
  • Exceptions in destinations are now handled better: instead of being dropped silently an attempt is made to log a message about the problem. If that also fails then the exception is dropped.



Incompatible output format change! In previous versions the ordering of messages and actions was ambiguous and could not be deduced from out-of-order logs, and even where it was possible sorting correctly was difficult. To fix this the action_counter field was removed and now all messages can be uniquely located within a specific task by the values in an improved task_level field.


  • Eliot tasks can now span multiple processes and threads, allowing for easy tracing of actions in complex and distributed applications.
  • eliot.add_global_fields allows adding fields with specific values to all Eliot messages logged by your program. This can be used to e.g. distinguish between log messages from different processes by including relevant identifying information.

Bug fixes:

  • On Python 3 files that accept unicode (e.g. sys.stdout) should now work.



  • Added support for Python 3.4.
  • Most public methods and functions now have underscore-based equivalents to the camel case versions, e.g. eliot.write_traceback and eliot.writeTraceback, for use in PEP 8 styled programs. Twisted-facing APIs and pyunit assertions do not provide these additional APIs, as camel-case is the native idiom.
  • eliot.to_file outputs log messages to a file.
  • Documented how to load Eliot logging into ElasticSearch via Logstash.
  • Documentation has been significantly reorganized.


Note that this is the last release that will make incompatible API changes without interim deprecation warnings.

Incompatible changes from 0.3.0:

  • Logger no longer does JSON serialization; it’s up to destinations to decide how to serialize the dictionaries they receive.
  • Timestamps are no longer encoded in TAI64N format; they are now provided as seconds since the Unix epoch.
  • ActionType no longer supports defining additional failure fields, and therefore accepts one argument less.
  • Action.runCallback and Action.finishAfter have been removed, as they are replaced by DeferredContext (see below).


  • Added a simpler API (fields()) for defining fields for ActionType and MessageType.
  • Added support for Python 3.3.
  • Actions can now be explicitly finished using a public API: Action.finish().
  • Action.context() context manager allows setting an action context without finishing the action when exiting the block.
  • Added a new API for Twisted Deferred support: eliot.twisted.DeferredContext.
  • eliot.twisted.redirectLogsForTrial will redirect Eliot logs to Twisted’s logs when running under the trial test runner.