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Solve the following problem using Python, implementing the functions described below, one line at a time
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<USER_TASK:>
Description:
 def verify(cls, user_id, verification_hash):
 """ Verify a user using the verification hash The verification hash is removed from the user once verified :param user_id: the user ID :param verification_hash: the verification hash :returns: a User instance """

        user = yield cls.get(user_id)

        # If user does not have verification hash then this means they have already been verified
        if 'verification_hash' not in user._resource:
            raise Return(user)

        if user.verification_hash != verification_hash:
            raise exceptions.ValidationError('Invalid verification hash')

        del user.verification_hash
        yield user._save()

        raise Return(user)