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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 mutate(self, field):
 """Mutate the given field, modifying it directly. This is not intended to preserve the value of the field. :field: The pfp.fields.Field instance that will receive the new value """

        new_val = self.next_val(field)
        field._pfp__set_value(new_val)
        return field