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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 subdomain(self, domain, depth):
 """ Return so-called subdomain of specified depth in the private suffix. """

        p = self.privateparts(domain)
        if p is None or depth > len(p) - 1:
            return None
        else:
            return ".".join(p[-(depth+1):])