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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 field_from_json(self, key_and_type, json_value):
 """Convert a JSON-serializable representation back to a field."""

        assert ':' in key_and_type
        key, type_code = key_and_type.split(':', 1)
        from_json = self.field_function(type_code, 'from_json')
        value = from_json(json_value)
        return key, value