def synchronize(self, delete=False):
        """Synchronize the localpath to S3.

        Upload new or changed files.
        Delete files that no longer exist locally."""
        bucket = self.get_bucket()
        s3_paths = s3_util.get_paths_from_keys(bucket)
        local_files = set()
        for dirpath, dirnames, filenames in os.walk(self.localpath):
            for filename in filenames:
                file_path = os.path.join(dirpath,filename)
                file_key = os.path.relpath(file_path,self.localpath)
                if os.sep == "\\":
                    #Windows paths need conversion
                    file_key = file_key.replace("\\","/")
                local_files.add(file_key)
                try:
                    s3_key = s3_paths[file_key]
                except KeyError:
                    #File is new
                    s3_key = bucket.new_key(file_key)
                    logger.info("Uploading new file: {0}".format(file_key))
                    s3_key.set_contents_from_filename(file_path)
                    s3_key.set_acl("public-read")
                else:
                    #File already exists, check if it's changed.
                    local_md5 = util.md5_for_file(file_path)
                    if local_md5 != s3_key.etag.replace("\"",""):
                        #File has changed
                        logger.info("Uploading changed file: {0}".format(file_key))
                        s3_key.set_contents_from_filename(file_path)
                        s3_key.set_acl("public-read")
        if delete:
            #Delete all files that don't exist locally
            for name, key in s3_paths.items():
                if name not in local_files:
                    #Delete it.
                    logger.info("Deleting old file: {0}".format(name))
                    key.delete()