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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 fof(self, linkinglength, out=None, method='splay'):
 """ Friend-of-Friend clustering with linking length. Returns: the label """

        if out is None:
            out = numpy.empty(self.size, dtype='intp')
        return _core.KDNode.fof(self, linkinglength, out, method)