code: def _close(self, fd):
          
          try:
              self.files[fd].close()
              self._closed_files.append(self.files[fd])  # Keep track for SymbolicFile testcase generation
              self.files[fd] = None
          except IndexError:
              raise FdError(f"Bad file descriptor ({fd})")
docs: Removes a file descriptor from the file descriptor list
          :rtype: int
          :param fd: the file descriptor to close.
          :return: C{0} on success.