# Errors and Diagnostics¶

## Logging¶

LensKit algorithms and evaluation routines report diagnostic data using the standard Python logging framework. Loggers are named after the corresponding Python module, and all live under the lenskit namespace.

Algorithms usually report erroneous or anomalous conditions using Python exceptions and warnings. Evaluation code, such as that in lenskit.batch, typically reports such conditions using the logger, as the common use case is to be running them in a script.

## Warnings¶

In addition to Python standard warning types such as warnings.DeprecationWarning, LensKit uses the following warning classes to report anomalous problems in use of LensKit.

class lenskit.DataWarning

Warning raised for detectable problems with input data.