code: def s3_download(output_file_path, s3_bucket, s3_access_key_id, s3_secret_key,
                  s3_file_key=None, prefix=None):
      
      bucket = s3_connect(s3_bucket, s3_access_key_id, s3_secret_key)
      if not s3_file_key:
          keys = s3_list(s3_bucket, s3_access_key_id, s3_secret_key, prefix)
          if not keys:
              raise Exception("Target S3 bucket is empty")
          s3_file_key = keys[-1]
      key = Key(bucket, s3_file_key)
      with open(output_file_path, "w+") as f:
          f.write(key.read())
docs: Downloads the file matching the provided key, in the provided bucket,
          from Amazon S3.
          
          If s3_file_key is none, it downloads the last file
          from the provided bucket with the .tbz extension, filtering by
          prefix if it is provided.