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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 query(self):
 """A mongdb query expression to find all records with higher values for this mark's fields in the collection. :rtype: dict """

        q = {}
        for field, value in self._pos.items():
            if value is None:
                q.update({field: {'$exists': True}})
            else:
                q.update({field: {'$gt': value}})
        return q