code: def split_extension(file_name, special=['tar.bz2', 'tar.gz']):
      
      file_name = str(file_name)
  
      if file_name.endswith(tuple(special)):
          for end in special:
              if file_name.endswith(end):
                  return end
      return file_name.split('.')[-1]
docs: Find the file extension of a file name, including support for
      special case multipart file extensions (like .tar.gz)
  
      Parameters
      ----------
      file_name: str, file name
      special:   list of str, multipart extensions
                 eg: ['tar.bz2', 'tar.gz']
  
      Returns
      ----------
      extension: str, last characters after a period, or
                 a value from 'special'