Package roslib
source code
roslib has a very important role in all Python code written for ROS:
it contains the load_manifest() method, which updates the PYTHONPATH
based on a set of ROS Package manifest.xml files. Because of this role,
roslib is required to be on the PYTHONPATH of every ROS installation.
Beyond the important load_manifest() call, most of the rest of roslib
consists of low-level libraries that 99% of ROS users need not interact
with. These libraries are primarily to support higher-level ROS Python
libraries, such as the rospy client library, as well as numerous ROS
tools (e.g. rostopic).