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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 ajax_list_catalog(self, catid):
        '''
        Get posts of certain catid. In Json.

        根据分类ID（catid）获取 该分类下 post 的相关信息，返回Json格式
        '''
        out_arr = {}
        for catinfo in MPost2Catalog.query_postinfo_by_cat(catid):
            out_arr[catinfo.uid] = catinfo.title

        json.dump(out_arr, self)