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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):
 """Serialize all the fields into one string."""


        keys = self._all_keys()
        serdata = {}
        for fieldname, value in self._data.items():
            serdata[fieldname] = getattr(type(self), fieldname).python_to_cache(value)
        return json.dumps(serdata)