docs: def prepend_to_file(path, data, bufsize=1<<15):
      """TODO:
      * Add a random string to the backup file.
      * Restore permissions after copy.
      """
      # Backup the file #
      backupname = path + os.extsep + 'bak'
      # Remove previous backup if it exists #
      try: os.unlink(backupname)
      except OSError: pass
      os.rename(path, backupname)
      # Open input/output files,  note: outputfile's permissions lost #
      with open(backupname) as inputfile:
          with open(path, 'w') as outputfile:
              outputfile.write(data)
              buf = inputfile.read(bufsize)
              while buf:
                  outputfile.write(buf)
                  buf = inputfile.read(bufsize)
      # Remove backup on success #
      os.remove(backupname)