'Create a L{Bucket} that may have a parent L{Bucket}.
@param parentBucket: If a parent Bucket is specified,
all L{add} and L{drip} operations on this L{Bucket}
will be applied on the parent L{Bucket} as well.
@type parentBucket: L{Bucket}'

def __init__(self, parentBucket=None):

    self.content = 0
    self.parentBucket = parentBucket
    self.lastDrip = time()
