# 3.10.4. Change Sources

## 3.10.4.1. ChangeSource

class buildbot.changes.base.ChangeSource

  This is the base class for change sources.

  Subclasses should override the inherited `activate` and `deactivate` methods if necessary to handle initialization and shutdown.

  Change sources which are active on every master should, instead, override `startService` and `stopService`.

## 3.10.4.2. ReconfigurablePollingChangeSource

class buildbot.changes.base.ReconfigurablePollingChangeSource

  This is a subclass of `ChangeSource` which adds polling behavior. Its constructor accepts the `pollInterval` and `pollAtLaunch` arguments as documented for most built-in change sources.

  Subclasses should override the `poll` method. This method may return a Deferred. Calls to `poll` will not overlap.