class ROSBagException(Exception):
    """
    Base class for exceptions in rosbag.
    """
    pass
 
class ROSBagFormatException(ROSBagException):
    """
    Exceptions for errors relating to the bag file format.
    """
    pass

class ROSBagUnindexedException(ROSBagException):
    """
    Exception for unindexed bags.
    """
    def __init__(self, *args):
        ROSBagException.__init__(self, 'Unindexed bag')