All notable changes to this project will be documented in this file.

The format is based on Keep a Changelog and this project adheres to Calendar Versioning.

The first number of the version is the year. The second number is incremented with each release, starting at 1 for each year. The third number is for emergencies when we need to start branches for older releases.

You can find out backwards-compatibility policy here.

23.1.0 - 2023-04-06#


  • structlog.stdlib.BoundLogger now has, analogously to our native logger, a full set of async log methods prefixed with an a: await log.ainfo("event!") #502

  • The default configuration now respects the presence of FORCE_COLOR (regardless of its value, unless an empty string). This disables all heuristics whether it makes sense to use colors. #503

  • The default configuration now respects the presence of NO_COLOR (regardless of its value, unless an empty string). This disables all heuristics whether it makes sense to use colors and overrides FORCE_COLOR. #504


  • ConsoleRenderer now reuses the _figure_out_exc_info to process the exc_info argument like ExceptionRenderer does. This prevents crashes if the actual Exception is passed for the exc_info argument instead of a tuple or True. #482

  • FilteringBoundLogger.aexception() now extracts the exception info using sys.exc_info() before passing control to the asyncio executor (where original exception info is no longer available). #488

22.3.0 - 2022-11-24#


  • String interpolation in FilteringBoundLogger (used by default) is now only attempted if positional arguments are passed. This prevents crashes if something different than a string is passed for the event argument. #475


  • String interpolation doesn’t cause crashes in filtered log call anymore. #478

22.2.0 - 2022-11-19#


  • Accessing package metadata as attributes on the structlog module is deprecated (e.g. structlog.__version__). Please use importlib.metadata instead (for Python 3.7: the importlib-metadata PyPI package).

  • The structlog.types module is now deprecated in favor of the structlog.typing module. It seems like the Python typing community is settling on this name.


  • FilteringBoundLogger (used by default) now allows for string interpolation using positional arguments:

    >>>"Hello %s! The answer is %d.", "World", 42, x=1)
    2022-10-07 10:04.31 [info     ] Hello World! The answer is 42. x=1


  • FilteringBoundLogger now also has support for asyncio-based logging. Instead of a wrapper class like structlog.stdlib.AsyncBoundLogger, async equivalents have been added for all logging methods. So instead of"hello") you can also write await log.ainfo("hello") in async functions and methods.

    This seems like the better approach and if it’s liked by the community, structlog.stdlib.BoundLogger will get those methods too. #457


  • The documentation has been heavily overhauled. Have a look if you haven’t lately! Especially the graphs in the standard library chapter have proven valuable to many.

  • The build backend has been switched to Hatch.


  • The timestamps in the default configuration now use the correct separator (:) for seconds.

22.1.0 - 2022-07-20#


  • Python 3.6 is not supported anymore.

  • Pickling is now only possible with protocol version 3 and newer.


  • The entire structlog.threadlocal module is deprecated. Please use the primitives from structlog.contextvars instead.

    If you’re using the modern APIs (bind_threadlocal() / merge_threadlocal()) it’s enough to replace them 1:1 with their contextvars counterparts. The old approach around wrap_dict() has been discouraged for a while.

    Currently there are no concrete plans to remove the module, but no patches against it will be accepted from now on. #409


  • structlog.processors.StackInfoRenderer now has an additional_ignores parameter that allows you to filter out your own logging layer. #396

  • Added structlog.WriteLogger, a faster – but more low-level – alternative to structlog.PrintLogger. It works the way PrintLogger used to work in previous versions. #403 #404

  • structlog.make_filtering_bound_logger()-returned loggers now also have a log() method to match the structlog.stdlib.BoundLogger signature closer. #413

  • Added structured logging of tracebacks via the structlog.tracebacks module, and most notably the structlog.tracebacks.ExceptionDictTransformer which can be used with the new structlog.processors.ExceptionRenderer to render JSON tracebacks. #407

  • structlog.stdlib.recreate_defaults(log_level=logging.NOTSET) that recreates structlog’s defaults on top of standard library’s logging. It optionally also configures logging to log to standard out at the passed log level. #428

  • structlog.processors.EventRenamer allows you to rename the hitherto hard-coded event dict key event to something else. Optionally, you can rename another key to event at the same time, too. So adding EventRenamer(to="msg", replace_by="_event") to your processor pipeline will rename the standard event key to msg and then rename the _event key to event. This allows you to use the event key in your own log files and to have consistent log message keys across languages.

  •"event") now allows to customize the name of the key that is used for the log message.


  • structlog.make_filtering_bound_logger() now returns a method with the same signature for all log levels, whether they are active or not. This ensures that invalid calls to inactive log levels are caught immediately and don’t explode once the log level changes. #401

  • structlog.PrintLogger – that is used by default – now uses print() for printing, making it a better citizen for interactive terminal applications. #399

  • structlog.testing.capture_logs now works for already initialized bound loggers. #408

  • structlog.processors.format_exc_info() is no longer a function, but an instance of structlog.processors.ExceptionRenderer. Its behavior has not changed. #407

  • The default configuration now includes the structlog.contextvars.merge_contextvars processor. That means you can use structlog.contextvars features without configuring structlog.


  • Overloaded the bind, unbind, try_unbind and new methods in the FilteringBoundLogger Protocol. This makes it easier to use objects of type FilteringBoundLogger in a typed context. #392

  • Monkeypatched sys.stdouts are now handled more gracefully by ConsoleRenderer (that’s used by default). #404

  • structlog.stdlib.render_to_log_kwargs() now correctly handles the presence of exc_info, stack_info, and stackLevel in the event dictionary. They are transformed into proper keyword arguments instead of putting them into the extra dictionary. #424, #427

21.5.0 - 2021-12-16#


  • Added the structlog.processors.LogfmtRenderer processor to render log lines using the logfmt format. #376

  • Added the structlog.stdlib.ExtraAdder processor that adds extra attributes of logging.LogRecord objects to the event dictionary. This processor can be used for adding data passed in the extra parameter of the logging module’s log methods to the event dictionary. #209, #377

  • Added the structlog.processor.CallsiteParameterAdder processor that adds parameters of the callsite that an event dictionary originated from to the event dictionary. This processor can be used to enrich events dictionaries with information such as the function name, line number and filename that an event dictionary originated from. #380

21.4.0 - 2021-11-25#


  • Added the structlog.threadlocal.bound_threadlocal and structlog.contextvars.bound_contextvars decorator/context managers to temporarily bind key-value pairs to a thread-local and context-local context. #371


  • Fixed import when running in optimized mode (PYTHONOPTIMIZE=2 or python -OO) . #373

21.3.0 - 2021-11-20#


  • now has sort_keys boolean parameter that allows to disable the sorting of keys on output. #358


  • structlog switched its packaging to flit. Users shouldn’t notice a difference, but (re-)packagers might.

  • structlog.stdlib.AsyncBoundLogger now determines the running loop when logging, not on instantiation. That has a minor performance impact, but makes it more robust when loops change (e.g. aiohttp.web.run_app()), or you want to use sync_bl before a loop has started.


  • structlog.processors.TimeStamper now works well with FreezeGun even when it gets applied before the loggers are configured. #364

  • structlog.stdlib.ProcessorFormatter now has a processors argument that allows to define a processor chain to run over all log entries.

    Before running the chain, two additional keys are added to the event dictionary: _record and _from_structlog. With them it’s possible to extract information from logging.LogRecords and differentiate between structlog and logging log entries while processing them.

    The old processor (singular) parameter is now deprecated, but no plans exist to remove it. #365

21.2.0 - 2021-10-12#


  • structlog.threadlocal.get_threadlocal() and structlog.contextvars.get_contextvars() can now be used to get a copy of the current thread-local/context-local context that has been bound using structlog.threadlocal.bind_threadlocal() and structlog.contextvars.bind_contextvars(). #331, #337

  • structlog.threadlocal.get_merged_threadlocal(bl) and structlog.contextvars.get_merged_contextvars(bl) do the same, but also merge the context from a bound logger bl. Same pull requests as previous change.

  • structlog.contextvars.bind_contextvars() now returns a mapping of keys to contextvars.Tokens, allowing you to reset values using the new structlog.contextvars.reset_contextvars(). #339

  • Exception rendering in is now configurable using the exception_formatter setting. If either the Rich or the better-exceptions package is present, structlog will use them for pretty-printing tracebacks. Rich takes precedence over better-exceptions if both are present.

    This only works if format_exc_info is absent in the processor chain. #330, #349

  • The final processor can now return a bytearray (additionally to str and bytes). #344


  • To implement pretty exceptions (see Changes below), now formats exceptions itself.

    Make sure to remove format_exc_info from your processor chain if you configure structlog manually. This change is not really breaking, because the old use-case will keep working as before. However if you pass pretty_exceptions=True (which is the default if either rich or better-exceptions is installed), a warning will be raised and the exception will be rendered without prettification.

  • All use of Colorama on non-Windows systems has been excised. Thus, colors are now enabled by default in on non-Windows systems. You can keep using Colorama to customize colors, of course. #345


  • structlog is now importable if sys.stdout is None (e.g. when running using pythonw). #313

21.1.0 - 2021-02-18#


  • will now look for a logger_name key if no logger key is set. #295


  • structlog.threadlocal.wrap_dict() now has a correct type annotation. #290

  • Fix isolation in structlog.contextvars. #302

  • The default configuration and loggers are pickleable again. #301

20.2.0 - 2020-12-31#


  • Python 2.7 and 3.5 aren’t supported anymore. The package meta data should ensure that you keep getting 20.1.0 on those versions. #244


  • Accessing the _context attribute of a bound logger is now deprecated. Please use the new structlog.get_context().


  • structlog has now type hints for all of its APIs! Since structlog is highly dynamic and configurable, this led to a few concessions like a specialized structlog.stdlib.get_logger() whose only difference to structlog.get_logger() is that it has the correct type hints.

    We consider them provisional for the time being – i.e. the backwards-compatibility does not apply to them in its full strength until we feel we got it right. Please feel free to provide feedback! #223, #282

  • Added structlog.make_filtering_logger that can be used like configure(wrapper_class=make_filtering_bound_logger(logging.INFO)). It creates a highly optimized bound logger whose inactive methods only consist of a return None. This is now also the default logger.

  • As a complement, structlog.stdlib.add_log_level() can now additionally be imported as structlog.processors.add_log_level since it just adds the method name to the event dict.

  • Added structlog.BytesLogger to avoid unnecessary encoding round trips. Concretely this is useful with orjson which returns bytes. #271

  • The final processor now also may return bytes that are passed untouched to the wrapped logger.

  • structlog.get_context() allows you to retrieve the original context of a bound logger. #266,

  • Added structlog.testing.CapturingLogger for more unit testing goodness.

  • Added structlog.stdlib.AsyncBoundLogger that executes logging calls in a thread executor and therefore doesn’t block. #245


  • The default bound logger (wrapper_class) if you don’t configure structlog has changed. It’s mostly compatible with the old one but a few uncommon methods like log, failure, or err don’t exist anymore.

    You can regain the old behavior by using structlog.configure(wrapper_class=structlog.BoundLogger).

    Please note that due to the various interactions between settings, it’s possible that you encounter even more errors. We strongly urge you to always configure all possible settings since the default configuration is not covered by our backwards-compatibility policy.

  • structlog.processors.add_log_level() is now part of the default configuration.

  • structlog.stdlib.ProcessorFormatter no longer uses exceptions for control flow, allowing foreign_pre_chain processors to use sys.exc_info() to access the real exception.


  • structlog.PrintLogger now supports copy.deepcopy(). #268

20.1.0 - 2020-01-28#


  • This is the last version to support Python 2.7 (including PyPy) and 3.5. All following versions will only support Python 3.6 or later.


  • Added a new module structlog.contextvars that allows to have a global but context-local structlog context the same way as with structlog.threadlocal since 19.2.0. #201, #236

  • Added a new module structlog.testing for first class testing support. The first entry is the context manager capture_logs() that allows to make assertions about structured log calls. #14, #234

  • Added structlog.threadlocal.unbind_threadlocal(). #239


  • The logger created by structlog.get_logger() is not detected as an abstract method anymore, when attached to an abstract base class. #229

  • Colorama isn’t initialized lazily on Windows anymore because it breaks rendering. #232, #242

19.2.0 - 2019-10-16#


  • Python 3.4 is not supported anymore. It has been unsupported by the Python core team for a while now and its PyPI downloads are negligible.

    It’s very unlikely that structlog will break under 3.4 anytime soon, but we don’t test it anymore.


  • Full Python 3.8 support for structlog.stdlib.

  • Added more pass-through properties to structlog.stdlib.BoundLogger. To makes it easier to use it as a drop-in replacement for logging.Logger. #198

  • Added new processor that will set exc_info=True if the method’s name is exception and exc_info isn’t set at all. This is only necessary when the standard library integration is not used. It fixes the problem that in the default configuration, structlog.get_logger().exception("hi") in an except block would not print the exception without passing exc_info=True to it explicitly. #130, #173, #200, #204

  • Added a new thread-local API that allows binding values to a thread-local context explicitly without affecting the default behavior of bind(). #222, #225

  • Added pass_foreign_args argument to structlog.stdlib.ProcessorFormatter. It allows to pass a foreign log record’s args attribute to the event dictionary under the positional_args key. #228


  • structlog.stdlib.ProcessorFormatter now takes a logger object as an optional keyword argument. This makes ProcessorFormatter work properly with stuctlog.stdlib.filter_by_level(). #219

  • now calls str() on the event value. #221


  • now uses no colors by default, if Colorama is not available. #215

  • now initializes Colorama lazily, to prevent accidental side-effects just by importing structlog. #210

  • A best effort has been made to make as much of structlog pickleable as possible to make it friendlier with multiprocessing and similar libraries. Some classes can only be pickled on Python 3 or using the dill library though and that is very unlikely to change.

    So far, the configuration proxy, structlog.processor.TimeStamper, structlog.BoundLogger, structlog.PrintLogger and have been made pickleable. Please report if you need any another class fixed. #126

19.1.0 - 2019-02-02#


  • structlog.ReturnLogger and structlog.PrintLogger now have a fatal() log method. #181


  • As announced in 18.1.0, pip install -e .[dev] now installs all development dependencies. Sorry for the inconveniences this undoubtedly will cause!

  • structlog now tolerates passing through dicts to stdlib logging. #187, #188, #189


  • Under certain (rather unclear) circumstances, the frame extraction could throw an SystemError: error return without exception set. A workaround has been added. #174

18.2.0 - 2018-09-05#


  • Added structlog.stdlib.add_log_level_number() processor that adds the level number to the event dictionary. Can be used to simplify log filtering. #151

  • structlog.processors.JSONRenderer now allows for overwriting the default argument of its serializer. #77, #163

  • Added try_unbind() that works like unbind() but doesn’t raise a KeyError if one of the keys is missing. #171

18.1.0 - 2018-01-27#


  • The meaning of the structlog[dev] installation target will change from “colorful output” to “dependencies to develop structlog” in 19.1.0.

    The main reason behind this decision is that it’s impossible to have a structlog in your normal dependencies and additionally a structlog[dev] for development (pip will report an error).


  • now accepts a force_colors argument to output colored logs even if the destination is not a tty. Use this option if your logs are stored in files that are intended to be streamed to the console.

  • now accepts a level_styles argument for overriding the colors for individual levels, as well as to add new levels. See the docs for ConsoleRenderer.get_default_level_styles() for usage. #139

  • Added structlog.is_configured() to check whether or not structlog has been configured.

  • Added structlog.get_config() to introspect current configuration.


  • Empty strings are valid events now. #110

  • structlog.stdlib.BoundLogger.exception() now uses the exc_info argument if it has been passed instead of setting it unconditionally to True. #149

  • Default configuration now uses plain dicts on Python 3.6+ and PyPy since they are ordered by default.


  • Do not encapsulate Twisted failures twice with newer versions of Twisted. #144

17.2.0 - 2017-05-15#


  • structlog.stdlib.ProcessorFormatter now accepts keep_exc_info and keep_stack_info arguments to control what to do with this information on log records. Most likely you want them both to be False therefore it’s the default. #109


  • structlog.stdlib.add_logger_name() now works in structlog.stdlib.ProcessorFormatter’s foreign_pre_chain. #112

  • Clear log record args in structlog.stdlib.ProcessorFormatter after rendering. This fix is for you if you tried to use it and got TypeError: not all arguments converted during string formatting exceptions. #116, #117

17.1.0 - 2017-04-24#

The main features of this release are massive improvements in standard library’s logging integration. Have a look at the updated standard library chapter on how to use them! Special thanks go to Fabian Büchler, Gilbert Gilb’s, Iva Kaneva, insolite, and sky-code, that made them possible.


  • Added structlog.stdlib.render_to_log_kwargs(). This allows you to use logging-based formatters to take care of rendering your entries. #98

  • Added structlog.stdlib.ProcessorFormatter which does the opposite: This allows you to run structlog processors on arbitrary logging.LogRecords. #79, #105

  • Added repr_native_str to structlog.processors.KeyValueRenderer and This allows for human-readable non-ASCII output on Python 2 (repr() on Python 2 behaves like ascii() on Python 3 in that regard). As per compatibility policy, it’s on (original behavior) in KeyValueRenderer and off (human-friendly behavior) in ConsoleRenderer. #94

  • Added colors argument to and made it the default renderer. #78


  • The default renderer now is if you don’t configure structlog. Colors are used if available and human-friendly timestamps are prepended. This is in line with our backwards-compatibility policy that explicitly excludes default settings.

  • UNIX epoch timestamps from structlog.processors.TimeStamper are more precise now.

  • Positional arguments are now removed even if they are empty. #82


  • Fixed bug with Python 3 and structlog.stdlib.BoundLogger.log(). Error log level was not reproducible and was logged as exception one time out of two. #92

16.1.0 - 2016-05-24#


  • Python 3.3 and 2.6 aren’t supported anymore. They may work by chance but any effort to keep them working has ceased.

    The last Python 2.6 release was on October 29, 2013 and isn’t supported by the CPython core team anymore. Major Python packages like Django and Twisted dropped Python 2.6 a while ago already.

    Python 3.3 never had a significant user base and wasn’t part of any distribution’s LTS release.


  • Added a drop_missing argument to KeyValueRenderer. If key_order is used and a key is missing a value, it’s not rendered at all instead of being rendered as None. #67


  • Exceptions without a __traceback__ are now also rendered on Python 3.

  • Don’t cache loggers in lazy proxies returned from get_logger(). This lead to in-place mutation of them if used before configuration which in turn lead to the problem that configuration was applied only partially to them later. #72

16.0.0 - 2016-01-28#


  • Added that renders the event dictionary aligned and with colors.

  • Added structlog.processors.UnicodeDecoder that will decode all byte string values in an event dictionary to Unicode.

  • Added serializer parameter to structlog.processors.JSONRenderer which allows for using different (possibly faster) JSON encoders than the standard library.


  • structlog.processors.ExceptionPrettyPrinter and structlog.processors.format_exc_info now support passing of Exceptions on Python 3.

  • six is now used for compatibility.


  • The context is now cleaned up when exiting structlog.threadlocal.tmp_bind in case of exceptions. #64

  • Be more more lenient about missing __name__s. #62

15.3.0 - 2015-09-25#


  • Officially support Python 3.5.

  • Added structlog.ReturnLogger.failure and structlog.PrintLogger.failure as preparation for the new Twisted logging system.


  • Tolerate frames without a __name__, better. #58

15.2.0 - 2015-06-10#


  • Added option to specify target key in structlog.processors.TimeStamper processor. #51


  • Allow empty lists of processors. This is a valid use case since #26 has been merged. Before, supplying an empty list resulted in the defaults being used.

  • Better support of logging.Logger.exception within structlog. #52


  • Prevent Twisted’s log.err from quoting strings rendered by structlog.twisted.JSONRenderer.

15.1.0 - 2015-02-24#


  • Tolerate frames without a __name__ when guessing callsite names.

15.0.0 - 2015-01-23#


  • Added structlog.stdlib.add_log_level and structlog.stdlib.add_logger_name processors. #44

  • Added structlog.stdlib.BoundLogger.log. #42

  • Added structlog.stdlib.BoundLogger.exception. #22


  • Pass positional arguments to stdlib wrapped loggers that use string formatting. #19

  • structlog is now dually licensed under the Apache License, Version 2 and the MIT license. Therefore it is now legal to use structlog with GPLv2-licensed projects. #28

0.4.2 - 2014-07-26#


  • Drop support for Python 3.2. There is no justification to add complexity for a Python version that nobody uses. If you are one of the 0.350% that use Python 3.2, please stick to the 0.4 branch; critical bugs will still be fixed.


  • Officially support Python 3.4.

  • Allow final processor to return a dictionary. See the adapting chapter. #26

  • Test Twisted-related code on Python 3 (with some caveats).


  • Fixed a memory leak in greenlet code that emulates thread locals. It shouldn’t matter in practice unless you use multiple wrapped dicts within one program that is rather unlikely. #8

  • structlog.PrintLogger now is thread-safe.

  • from structlog import * works now (but you still shouldn’t use it).

0.4.1 - 2013-12-19#


  • Don’t cache proxied methods in structlog.threadlocal._ThreadLocalDictWrapper. This doesn’t affect regular users.


  • Various doc fixes.

0.4.0 - 2013-11-10#


  • Added structlog.processors.StackInfoRenderer for adding stack information to log entries without involving exceptions. Also added it to default processor chain. #6

  • Allow optional positional arguments for structlog.get_logger that are passed to logger factories. The standard library factory uses this for explicit logger naming. #12

  • Add structlog.processors.ExceptionPrettyPrinter for development and testing when multiline log entries aren’t just acceptable but even helpful.

  • Allow the standard library name guesser to ignore certain frame names. This is useful together with frameworks.

  • Add meta data (e.g. function names, line numbers) extraction for wrapped stdlib loggers. #5

0.3.2 - 2013-09-27#


  • Fix stdlib’s name guessing.

0.3.1 - 2013-09-26#


  • Added forgotten structlog.processors.TimeStamper to API documentation.

0.3.0 - 2013-09-23#


  • Greatly enhanced and polished the documentation and added a new theme based on Write The Docs, requests, and Flask.

  • Add Python Standard Library-specific BoundLogger that has an explicit API instead of intercepting unknown method calls. See structlog.stdlib.BoundLogger.

  • structlog.ReturnLogger now allows arbitrary positional and keyword arguments.

  • Add Twisted-specific BoundLogger that has an explicit API instead of intercepting unknown method calls. See structlog.twisted.BoundLogger.

  • Allow logger proxies that are returned by structlog.get_logger and structlog.wrap_logger to cache the BoundLogger they assemble according to configuration on first use. See the chapter on performance and the cache_logger_on_first_use argument of structlog.configure and structlog.wrap_logger.

  • Extract a common base class for loggers that does nothing except keeping the context state. This makes writing custom loggers much easier and more straight-forward. See structlog.BoundLoggerBase.

0.2.0 - 2013-09-17#


  • Add key_order option to structlog.processors.KeyValueRenderer for more predictable log entries with any dict class.

  • Enhance Twisted support by offering JSONification of non-structlog log entries.

  • Allow for custom serialization in structlog.twisted.JSONRenderer without abusing __repr__.


  • Promote to stable, thus henceforth a strict backwards-compatibility policy is put into effect.

  • structlog.PrintLogger now uses proper I/O routines and is thus viable not only for examples but also for production.

0.1.0 - 2013-09-16#

Initial release.