code: def size_str(size_in_bytes):
    
    if not size_in_bytes:
      return "?? GiB"
  
    size_in_bytes = float(size_in_bytes)
    for (name, size_bytes) in _NAME_LIST:
      value = size_in_bytes / size_bytes
      if value >= 1.0:
        return "{:.2f} {}".format(value, name)
    return "{} {}".format(int(size_in_bytes), "bytes")
docs: Returns a human readable size string.
  
    If size_in_bytes is None, then returns "?? GiB".
  
    For example `size_str(1.5 * tfds.units.GiB) == "1.50 GiB"`.
  
    Args:
      size_in_bytes: `int` or `None`, the size, in bytes, that we want to
        format as a human-readable size string.