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Structured Logging for Python

Project description

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structlog makes logging in Python less painful and more powerful by adding structure to your log entries.

It’s up to you whether you want structlog to take care about the output of your log entries or whether you prefer to forward them to an existing logging system like the standard library’s logging module. No monkey patching involved in either case.

Easier Logging

You can stop writing prose and start thinking in terms of an event that happens in the context of key/value pairs:

>>> from structlog import get_logger
>>> log = get_logger()
>>>"key_value_logging", out_of_the_box=True, effort=0)
2016-04-20 16:20.13 key_value_logging              effort=0 out_of_the_box=True

Each log entry is a meaningful dictionary instead of an opaque string now!

Data Binding

Since log entries are dictionaries, you can start binding and re-binding key/value pairs to your loggers to ensure they are present in every following logging call:

>>> log = log.bind(user="anonymous", some_key=23)
>>> log = log.bind(user="hynek", another_key=42)
>>>"user.logged_in", happy=True)
2016-04-20 16:20.13 user.logged_in                 another_key=42 happy=True some_key=23 user='hynek'

Powerful Pipelines

Each log entry goes through a processor pipeline that is just a chain of functions that receive a dictionary and return a new dictionary that gets fed into the next function. That allows for simple but powerful data manipulation:

def timestamper(logger, log_method, event_dict):
    """Add a timestamp to each log entry."""
    event_dict["timestamp"] = time.time()
    return event_dict

There are plenty of processors for most common tasks coming with structlog:


structlog is completely flexible about how the resulting log entry is emitted. Since each log entry is a dictionary, it can be formatted to any format:

  • A colorful key/value format for local development,
  • JSON for easy parsing,
  • or some standard format you have parsers for like nginx or Apache httpd.

Internally, formatters are processors whose return value (usually a string) is passed into loggers that are responsible for the output of your message. structlog comes with multiple useful formatters out of-the-box.


structlog is also very flexible with the final output of your log entries:

  • A built-in lightweight printer like in the examples above. Easy to use and fast.
  • Use the standard library’s or Twisted’s logging modules for compatibility. In this case structlog works like a wrapper that formats a string and passes them off into existing systems that won’t ever know that structlog even exists. Or the other way round: structlog comes with a logging formatter that allows for processing third party log records.
  • Don’t format it to a string at all! structlog passes you a dictionary and you can do with it whatever you want. Reported uses cases are sending them out via network or saving them in a database.

Project Information

structlog is dual-licensed under Apache License, version 2 and MIT, available from PyPI, the source code can be found on GitHub, the documentation at

structlog targets Python 2.7, 3.4 and newer, and PyPy.

If you need any help, visit us on #structlog on Freenode!

Release Information

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.

Backward-incompatible changes:

  • 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 backward compatibility policy that explicitly excludes default settings.


  • 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
  • UNIX epoch timestamps from structlog.processors.TimeStamper are more precise now.
  • Added repr_native_str to structlog.processors.KeyValueRenderer and This allows for human-readable non-ASCII output on Python 2 (repr() on Python 2 haves like ascii() on Python 3 in that regard). As per compatibility policy, it’s on (original behavior) in KeyValueRenderer and off (humand-friendly behavior) in ConsoleRenderer. #94
  • Added colors argument to and made it the default renderer. #78
  • Fixed bug with Python 3 and structlog.stdlib.BoundLogger.log(). Error log level was not reproductible and was logged as exception one time out of two. #92
  • Positional arguments are now removed even if they are empty. #82

Full changelog.


structlog is written and maintained by Hynek Schlawack. It’s inspired by previous work done by Jean-Paul Calderone and David Reid.

The development is kindly supported by Variomedia AG.

A full list of contributors can be found on GitHub’s overview. Some of them disapprove of the addition of thread local context data. :)

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