For what it's worth you could also write that as:

    result = ''
    for b in file_bytes_iterator:
      if b == '\0': break
      result += b
    if b != '\0':
      throw ValueError("String is unterminated")

And while we're one the subject, I would also really like to have a construction like:

    result = ''
    while b != '\0' for b in file_bytes_iterator:
      result += b
    if b != '\0':
      throw ValueError("String is unterminated")

but I fear opinion might be divided on that one.