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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 reassemble(cls, fields, document):
 """ Take a previously assembled document and reassemble the given set of fields for it in place. """

        for field_name in cls._instructions:
            if field_name in fields:
                maker = cls._instructions[field_name]
                with maker.target(document):
                    document[field_name] = maker()