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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 serialize(self):
 """ Produce YAML version of this catalog. Note that this is not the same as ``.yaml()``, which produces a YAML block referring to this catalog. """

        import yaml
        output = {"metadata": self.metadata, "sources": {},
                  "name": self.name}
        for key, entry in self.items():
            output["sources"][key] = entry._captured_init_kwargs
        return yaml.dump(output)