docs: def sizeof_fmt(num):
      """Turn number of bytes into human-readable str.
  
      Parameters
      ----------
      num : int
          The number of bytes.
  
      Returns
      -------
      size : str
          The size in human-readable format.
      """
      units = ['bytes', 'kB', 'MB', 'GB', 'TB', 'PB']
      decimals = [0, 0, 1, 2, 2, 2]
      if num > 1:
          exponent = min(int(log(num, 1024)), len(units) - 1)
          quotient = float(num) / 1024 ** exponent
          unit = units[exponent]
          num_decimals = decimals[exponent]
          format_string = '{0:.%sf} {1}' % (num_decimals)
          return format_string.format(quotient, unit)
      if num == 0:
          return '0 bytes'
      if num == 1:
          return '1 byte'