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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _checkFileExists(self):
 """ Verifies that the underlying file exists and sets the _exception attribute if not Returns True if the file exists. If self._fileName is None, nothing is checked and True is returned. """

        if self._fileName and not os.path.exists(self._fileName):
            msg = "File not found: {}".format(self._fileName)
            logger.error(msg)
            self.setException(IOError(msg))
            return False
        else:
            return True