tstringlogger

Adds support for using t-strings in log messages while preserving all interpolated values.

Usage example:

>>> import logging
>>> from tstringlogger import TStringLogRecord
>>> test1, test2 = "hello", "world"
>>>
>>> # Set the default log record factory to one that supports t-strings
>>> logging.setLogRecordFactory(TStringLogRecord)
>>>
>>> logging.info(t"{test1=}, {test2}")
INFO:root:test1='hello', world
>>>
>>> # Standard logging still works normally
>>> logging.info("test1=%r, %s", test1, test2)
INFO:root:test1='hello', world

In this example the log record that was produced by the t-string message will have the data from the t-string available as record.args. In this case that would be: {"test1": "hello", "test2": "world"}.

Extracting these values from the t-string allows other parts of the logging system to use the values just as if they were provided as parameters to a normal logging call.

[!NOTE] The request to add native t-string logging support to the standard library can be found here: https://github.com/python/cpython/issues/134394

Alternative methods

Using the TStringLogRecordMixin

If your application already uses a custom LogRecord class, the TStringLogRecordMixin can be used to easily add t-string functionality to it.

>>> import logging
>>> from tstringlogger import TStringLogRecordMixin
>>>
>>> # example custom logger that adds a tag to every message
>>> class MyCustomLogRecord(TStringLogRecordMixin, logging.LogRecord):
...     def getMessage(self):
...         msg = super().getMessage()  # get the formatting t-string
...         return f"[tag] {msg}"
>>>
>>> logging.setLogRecordFactory(MyCustomLogRecord)
>>> test1, test2 = "hello", "world"
>>> logging.info(t"{test1=}, {test2}")
INFO:root:[tag] test1='hello', world

Globally enable t-string support

Support for t-string logging can be globally enabled/disabled by calling tstringlogger.enable()/tstringlogger.disable(). This adds support for t-strings by directly patching the LogRecord.__init__ and LogRecord.getMessage functions.

>>> import logging
>>> import tstringlogger
>>>
>>> tstringlogger.enable()  # apply patches
>>>
>>> test1, test2 = "hello", "world"
>>> logging.info(t"{test1=}, {test2}")
INFO:root:test1='hello', world
>>>
>>> tstringlogger.disable()  # remove patches
>>> logging.info(t"{test1=}, {test2}")
INFO:root:Template(strings=('test1=', ', ', ''), interpolations=(Interpolation...

Related work

bracelogger is a library that allows using new-style string formatting in log messages instead of %-based formatting.