yourbucketname: is the name of the bucket you want to empty;
count=50 : is the number of object you want to delete at a time (this is 1000 by default, lower value (e.g. 50) are requested when you try to delete a highly populate bucket i.e. > 1 milion of objects)
Download code from here: emptyBucket.py, then edit the script in order to act on your bucket, and lower the page size if required.