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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 upstream(self, table, chrom_or_feat, start=None, end=None, k=1):
 """ Return k-nearest upstream features Parameters table : str or table table against which to query chrom_or_feat : str or feat either a chromosome, e.g. 'chr3' or a feature with .chrom, .start, .end attributes start : int if `chrom_or_feat` is a chrom, then this must be the integer start end : int if `chrom_or_feat` is a chrom, then this must be the integer end k : int number of upstream neighbors to return """

        res = self.knearest(table, chrom_or_feat, start, end, k, "up")
        end = getattr(chrom_or_feat, "end", end)
        start = getattr(chrom_or_feat, "start", start)
        rev = getattr(chrom_or_feat, "strand", "+") == "-"
        if rev:
            return [x for x in res if x.end > start]
        else:
            return [x for x in res if x.start < end]