code: def get_format_extension(fmt):
      '''
      Returns the recommended extension for a given format
      '''
  
      if fmt is None:
          return 'dict'
  
      fmt = fmt.lower()
      if fmt not in _converter_map:
          raise RuntimeError('Unknown basis set format "{}"'.format(fmt))
  
      return _converter_map[fmt]['extension'f get_format_extension(fmt):
      '''
      Returns the recommended extension for a given format
      '''
  
      if fmt is None:
          return 'dict'
  
      fmt = fmt.lower()
      if fmt not in _converter_map:
          raise RuntimeError('Unknown basis set format "{}"'.format(fmt))
  
      return _converter_map[fmt]['extension']
docs: Returns the recommended extension for a given format