---
id: extending-logging
title: Extending logging functionality
layout: docs
permalink: /docs/extending-logging.html
prev: best-practices.html
next: creating-new-operators.html
---

If you have already adopted some method for logging events, you may want to use that method to log experiment-related events, such as exposures and experiment-specific outcomes. You can do this by extending the `Experiment` abstract class and overriding the `log` method.

### Overriding the `log` method
To log exposures using your existing logging system, just override the `log`
method when extending the `Experiment` abstract class.
For example, if you write to your logs with `MySQLLogger`, then you might
reimplement `log` as follows.

```python

  def log(self, data):
    # self.MySQLLogger may be defined here or in configure_logger()
    self.MySQLLogger.log(data)

```

### Writing a log configuration method
Since all code in `log()` gets called every time a log event is triggered,
you may wish to set up a connection to your logging infrastructure in advance,
immediately before the first time you need to log the data.
To do this, you can override the `configure_logger()` method.

In `SimpleExperiment` configure_logger() actually sets a class variable, once
per experiment name, so that a connection to the logging module is only made
once per interpreter session.


### Adding caching
By default, each instance of an Experiment class will auto-exposure log once
per instance.  But this can still result in a lot of writing when there are
many instances created for a particular unit's assignment (for example,
  if an experiment parameter is retrieved each time a person loads the home
  page).
So you may want to add some caching (e.g., with memcache) to prevent
unnecessary logging. This can be done by overriding the `previously_logged()`
method.

### More information
Additional documentation for the `Experiment` class and `SimpleExperiment` class
can be found in the [source code](https://github.com/facebook/planout/blob/master/planout/experiment.py).