Count Integers in Intervals LeetCode solution in Python

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class CountIntervals:
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    def __init__(self):
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        # initialize the merged intervals list as below to handle edge cases
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        self.interv = [(-inf, -inf), (inf, inf)]
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        self.cov = 0
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    def add(self, left: int, right: int) -> None:
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        interv = self.interv
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        # find the left most position for inserting of the new potentially merged interval
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        # we use `left - 1` because the interval coverage is inclusive
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        li = bisect.bisect_left(interv, left - 1, key=itemgetter(1))
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        lval = min(interv[li][0], left)
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        # find the right most position for inserting the new potentially merged interval
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        # we use `right + 1` because the interval coverage is inclusive
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        ri = bisect.bisect_right(interv, right + 1, key=itemgetter(0))
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        rval = max(interv[ri - 1][1], right)
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        # find the coverage of the intervals that will be replaced by the new interval
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        to_delete = 0
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        for _ in range(li, ri):
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            to_delete += interv[_][1] - interv[_][0] + 1
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        # udpate the coverage
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        self.cov += rval - lval + 1 - to_delete
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        interv[li:ri] = [(lval, rval)]
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    def count(self) -> int:
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        return self.cov