'Delete the files in the cache that match the file name prefix,
if the prefix is None then all files will be deleted'

@staticmethod
def purgeCache(prefix=None):

    import os
    folder = ('applications%s/' % S3Chart.CACHE_PATH)
    if os.path.exists(folder):
        filelist = os.listdir(folder)
        for file in filelist:
            if ((prefix == None) or file.startswith(prefix)):
                os.remove(('%s%s' % (folder, file)))
