code: def download_file(self, file_path, store_directory=None):
          
          local_filename = file_path.split('/')[-1]
          if store_directory:
              local_filename = os.path.join(store_directory, local_filename)
          r = requests.get(
              '%s%s' % (self.url, 'DownloadFile'),
              params={'filePath': file_path},
              headers=self.headers,
              stream=True,
          )
          with open(local_filename, 'wb') as f:
              for chunk in r.iter_content(chunk_size=1024):
                  if chunk:
                      f.write(chunk)
          return local_filename
docs: Download a file from betfair historical and store in given directory or current directory.
          
          :param file_path: the file path as given by get_file_list method.
          :param store_directory: directory path to store data files in.
          :return: name of file.