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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 to_xml(self):
 """ Serialize all properties as XML """

        ret = '<exif>'
        for k in self.__dict__:
            ret += '<%s>%s</%s>' % (k, self.__dict__[k], k)
        ret += '</exif>'
        return ret