<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def indexed_file(self, f):
 """ Setter for information about the file this object indexes. :param f: a tuple of (filename, handle), either (or both) of which can be None. If the handle is None, but filename is provided, then handle is created from the filename. If both handle and filename are None, or they don't match the previous values indexed by this object, any current data in this index is cleared. If either are not None, we require the iterator and the hash function for this object to already be set. """

    filename, handle = f
    if handle is None and filename is not None:
      handle = open(filename)
    if (handle is None and filename is None) or \
       (filename != self._indexed_filename) or \
       (handle != self._indexed_file_handle):
      self.index = {}
    if ((handle is not None or filename is not None) and
       (self.record_iterator is None or self.record_hash_function is None)):
      raise IndexError("Setting index file failed; reason: iterator "
                       "(self.record_iterator) or hash function "
                       "(self.record_hash_function) have to be set first")
    self._indexed_filename = filename
    self._indexed_file_handle = handle