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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, message):
 """ Serialize the given message in-place, converting inputs to outputs. We do this in-place for performance reasons. There are more fields in a message than there are L{Field} objects because of the timestamp, task_level and task_uuid fields. By only iterating over our L{Fields} we therefore reduce the number of function calls in a critical code path. @param message: A C{dict}. """

        for key, field in self.fields.items():
            message[key] = field.serialize(message[key])