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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 update_default_values(self, **updates):
 """Replace the default values of specified fields. Parameters Parameters are taken as keyword-arguments of `field=new_value`. Raises ------ KeyError If a field doesn't exist in the struct. """

        for (field, value) in six.iteritems(updates):
            fname = six.b(field)
            self[fname] = self[fname]._replace(default=value)