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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 date_range_builder(self, start='2013-02-11', end=None):
 """ Builds date range query. :param start: Date string. format: YYYY-MM-DD :type start: String :param end: date string. format: YYYY-MM-DD :type end: String :returns: String """

        if not end:
            end = time.strftime('%Y-%m-%d')

        return 'acquisitionDate:[%s+TO+%s]' % (start, end)