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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 _binary_search_intervals(cls, intervals, index):
 """ Binary search for the interval containing index, assuming there is such an interval. This function should never return ``None``. """

        start = 0
        end = len(intervals) - 1
        while start <= end:
            middle_index = start + ((end - start) // 2)
            middle = intervals[middle_index]
            if (middle[0] <= index) and (index < middle[1]):
                return middle
            elif middle[0] > index:
                end = middle_index - 1
            else:
                start = middle_index + 1
        return None