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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 clusters(self):
 """ Returns known clusters by exposing as a read-only property. """

        if not hasattr(self, "_clusters"):
            cs = {}
            for cr in self.doc["clusters"]:
                cs[cr["name"]] = c = copy.deepcopy(cr["cluster"])
                if "server" not in c:
                    c["server"] = "http://localhost"
                BytesOrFile.maybe_set(c, "certificate-authority")
            self._clusters = cs
        return self._clusters