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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 _sincedb_start_position(self):
 """Retrieves the starting position from the sincedb sql db for a given file """

        if not self._sincedb_path:
            return None

        self._sincedb_init()
        self._log_debug('retrieving start_position from sincedb')
        conn = sqlite3.connect(self._sincedb_path, isolation_level=None)
        cursor = conn.cursor()
        cursor.execute('select position from sincedb where fid = :fid and filename = :filename', {
            'fid': self._fid,
            'filename': self._filename
        })

        start_position = None
        for row in cursor.fetchall():
            start_position, = row

        return start_position