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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 partition(self, nmin, nmax):
 """ This method call decomposes a QuadTree instances into a list of sub- QuadTree instances which are the smallest possible geospatial "buckets", given the current splitting rules, containing at least ``thresh`` points. Parameters thresh : int The minimum number of points per partition. Care should be taken not to set this parameter to be too low, as in large datasets a small cluster of highly adjacent points may result in a number of sub-recursive splits possibly in excess of Python's global recursion limit. Returns ------- partitions : list of QuadTree object instances A list of sub- QuadTree instances which are the smallest possible geospatial "buckets", given the current splitting rules, containing at least ``thresh`` points. """

        if self.n < nmin:
            return [self]
        else:
            ret = subpartition(self, nmin, nmax)
            return flatten(ret)