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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 query_region(self, chrom=None, start=None, stop=None):
 """Query the table, returning row or rows within the given genomic region. Parameters chrom : string, optional Chromosome/contig. start : int, optional Region start position (1-based). stop : int, optional Region stop position (1-based). Returns ------- result : VariantTable """

        if self.index is None:
            raise ValueError('no index has been set')
        if isinstance(self.index, SortedIndex):
            # ignore chrom
            loc = self.index.locate_range(start, stop)
        else:
            loc = self.index.locate_range(chrom, start, stop)
        return self[loc]