code: def _pad(expr, width, side='left', fillchar=' '):
      
  
      if not isinstance(fillchar, six.string_types):
          msg = 'fillchar must be a character, not {0}'
          raise TypeError(msg.format(type(fillchar).__name__))
  
      if len(fillchar) != 1:
          raise TypeError('fillchar must be a character, not str')
  
      if side not in ('left', 'right', 'both'):
          raise ValueError('Invalid side')
  
      return _string_op(expr, Pad, _width=width, _side=side, _fillchar=fillchar)
docs: Pad strings in the sequence or scalar with an additional character to specified side.
  
      :param expr:
      :param width: Minimum width of resulting string; additional characters will be filled with spaces
      :param side: {‘left’, ‘right’, ‘both’}, default ‘left’
      :param fillchar: Additional character for filling, default is whitespace
      :return: sequence or scalar