Structured Logging for Python
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.
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() >>> log.info("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!
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) >>> log.info("user.logged_in", happy=True) 2016-04-20 16:20.13 user.logged_in another_key=42 happy=True some_key=23 user='hynek'
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.
structlog targets Python 2.7, 3.4 and newer, and PyPy.
If you need any help, visit us on #structlog on Freenode!
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.
- The default renderer now is structlog.dev.ConsoleRenderer 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 structlog.dev.ConsoleRenderer. 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 structlog.dev.ConsoleRenderer 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
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