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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 filter_by(self, **kwargs):
 """ Apply the given filtering criterion to a copy of this Query, using keyword expressions. """

        query = self._copy()
        for field, value in kwargs.items():
            query.domain.append(
                (field, '=', value)
            )
        return query