<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def close_stream(self):
 """ Terminates an open stream and returns the filename of the file containing the streamed data. """

        if self.fout:
            fout = self.fout
            fout_fn = self.fout_fn
            self.fout.flush()
            self.fout.close()
            self.fout = None
            self.fout_fn = None
            return fout_fn