从MongoDB里面取得json格式的数据，然后存为本地的json文件，然后再从json读取变为dict

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天气预报在MongoDB中的天气预报的存储方式是：

/* 1 */
{
    "_id" : ObjectId("5a72ae6e6bd36a9f61e8ce3d"),
    "city" : "北京",
    "info" : [
        {
            "index_of_living" : [
                {
                    "assess" : "最弱",
                    "content" : "辐射弱，涂擦SPF8-12防晒护肤品。",
                    "name" : "紫外线指数"
                },
                {
                    "assess" : "较易波动",
                    "content" : "血糖较易波动，注意监测。",
                    "name" : "健臻·血糖指数"
                },
                {
                    "assess" : "较易发",
                    "content" : "温差较大，较易感冒，注意防护。",
                    "name" : "感冒指数"
                },
                {
                    "assess" : "冷",
                    "content" : "建议着棉衣加羊毛衫等冬季服装。",
                    "name" : "穿衣指数"
                },
                {
                    "assess" : "较适宜",
                    "content" : "无雨且风力较小，易保持清洁度。",
                    "name" : "洗车指数"
                },
                {
                    "assess" : "中",
                    "content" : "易感人群应适当减少室外活动。",
                    "name" : "空气污染扩散指数"
                }
            ],
            "K" : "5℃",
            "weather" : "晴转多云转晴",
            "time" : "1日（今天）",
            "wind" : "<3级转3-4级",
            "V" : "-7℃"
        },
        {
            "index_of_living" : [
                {
                    "assess" : "弱",
                    "content" : "辐射较弱，涂擦SPF12-15、PA+护肤品。",
                    "name" : "紫外线指数"
                },
                {
                    "assess" : "易波动",
                    "content" : "气温多变，血糖易波动，请注意监测。",
                    "name" : "健臻·血糖指数"
                },
                {
                    "assess" : "极易发",
                    "content" : "强降温，天气寒冷，极易发生感冒。",
                    "name" : "感冒指数"
                },
                {
                    "assess" : "寒冷",
                    "content" : "建议着厚羽绒服等隆冬服装。",
                    "name" : "穿衣指数"
                },
                {
                    "assess" : "较适宜",
                    "content" : "无雨且风力较小，易保持清洁度。",
                    "name" : "洗车指数"
                },
                {
                    "assess" : "良",
                    "content" : "气象条件有利于空气污染物扩散。",
                    "name" : "空气污染扩散指数"
                }
            ],
            "K" : "-1℃",
            "weather" : "晴",
            "time" : "2日（明天）",
            "wind" : "3-4级转<3级",
            "V" : "-9℃"
        },
        {
            "index_of_living" : [
                {
                    "assess" : "最弱",
                    "content" : "辐射弱，涂擦SPF8-12防晒护肤品。",
                    "name" : "紫外线指数"
                },
                {
                    "assess" : "易波动",
                    "content" : "血糖易波动，注意监测。",
                    "name" : "健臻·血糖指数"
                },
                {
                    "assess" : "较易发",
                    "content" : "天较凉，增加衣服，注意防护。",
                    "name" : "感冒指数"
                },
                {
                    "assess" : "冷",
                    "content" : "建议着棉衣加羊毛衫等冬季服装。",
                    "name" : "穿衣指数"
                },
                {
                    "assess" : "较适宜",
                    "content" : "无雨且风力较小，易保持清洁度。",
                    "name" : "洗车指数"
                },
                {
                    "assess" : "中",
                    "content" : "易感人群应适当减少室外活动。",
                    "name" : "空气污染扩散指数"
                }
            ],
            "K" : "0℃",
            "weather" : "多云",
            "time" : "3日（后天）",
            "wind" : "<3级",
            "V" : "-9℃"
        },
        {
            "index_of_living" : [
                {
                    "assess" : "弱",
                    "content" : "辐射较弱，涂擦SPF12-15、PA+护肤品。",
                    "name" : "紫外线指数"
                },
                {
                    "assess" : "易波动",
                    "content" : "血糖易波动，注意监测。",
                    "name" : "健臻·血糖指数"
                },
                {
                    "assess" : "较易发",
                    "content" : "天较凉，增加衣服，注意防护。",
                    "name" : "感冒指数"
                },
                {
                    "assess" : "冷",
                    "content" : "建议着棉衣加羊毛衫等冬季服装。",
                    "name" : "穿衣指数"
                },
                {
                    "assess" : "较适宜",
                    "content" : "无雨且风力较小，易保持清洁度。",
                    "name" : "洗车指数"
                },
                {
                    "assess" : "中",
                    "content" : "易感人群应适当减少室外活动。",
                    "name" : "空气污染扩散指数"
                }
            ],
            "K" : "1℃",
            "weather" : "晴",
            "time" : "4日（周日）",
            "wind" : "<3级",
            "V" : "-8℃"
        },
        {
            "index_of_living" : [
                {
                    "assess" : "弱",
                    "content" : "辐射较弱，涂擦SPF12-15、PA+护肤品。",
                    "name" : "紫外线指数"
                },
                {
                    "assess" : "易波动",
                    "content" : "血糖易波动，注意监测。",
                    "name" : "健臻·血糖指数"
                },
                {
                    "assess" : "较易发",
                    "content" : "天较凉，增加衣服，注意防护。",
                    "name" : "感冒指数"
                },
                {
                    "assess" : "冷",
                    "content" : "建议着棉衣加羊毛衫等冬季服装。",
                    "name" : "穿衣指数"
                },
                {
                    "assess" : "较适宜",
                    "content" : "无雨且风力较小，易保持清洁度。",
                    "name" : "洗车指数"
                },
                {
                    "assess" : "中",
                    "content" : "易感人群应适当减少室外活动。",
                    "name" : "空气污染扩散指数"
                }
            ],
            "K" : "0℃",
            "weather" : "晴",
            "time" : "5日（周一）",
            "wind" : "<3级",
            "V" : "-10℃"
        },
        {
            "index_of_living" : [
                {
                    "assess" : "弱",
                    "content" : "辐射较弱，涂擦SPF12-15、PA+护肤品。",
                    "name" : "紫外线指数"
                },
                {
                    "assess" : "较易波动",
                    "content" : "血糖较易波动，注意监测。",
                    "name" : "健臻·血糖指数"
                },
                {
                    "assess" : "较易发",
                    "content" : "天较凉，增加衣服，注意防护。",
                    "name" : "感冒指数"
                },
                {
                    "assess" : "冷",
                    "content" : "建议着棉衣加羊毛衫等冬季服装。",
                    "name" : "穿衣指数"
                },
                {
                    "assess" : "较适宜",
                    "content" : "无雨且风力较小，易保持清洁度。",
                    "name" : "洗车指数"
                },
                {
                    "assess" : "中",
                    "content" : "易感人群应适当减少室外活动。",
                    "name" : "空气污染扩散指数"
                }
            ],
            "K" : "2℃",
            "weather" : "晴",
            "time" : "6日（周二）",
            "wind" : "<3级",
            "V" : "-8℃"
        },
        {
            "index_of_living" : [
                {
                    "assess" : "弱",
                    "content" : "辐射较弱，涂擦SPF12-15、PA+护肤品。",
                    "name" : "紫外线指数"
                },
                {
                    "assess" : "较易波动",
                    "content" : "血糖较易波动，注意监测。",
                    "name" : "健臻·血糖指数"
                },
                {
                    "assess" : "较易发",
                    "content" : "天较凉，增加衣服，注意防护。",
                    "name" : "感冒指数"
                },
                {
                    "assess" : "冷",
                    "content" : "建议着棉衣加羊毛衫等冬季服装。",
                    "name" : "穿衣指数"
                },
                {
                    "assess" : "较适宜",
                    "content" : "无雨且风力较小，易保持清洁度。",
                    "name" : "洗车指数"
                },
                {
                    "assess" : "中",
                    "content" : "易感人群应适当减少室外活动。",
                    "name" : "空气污染扩散指数"
                }
            ],
            "K" : "3℃",
            "weather" : "晴转多云",
            "time" : "7日（周三）",
            "wind" : "<3级",
            "V" : "-8℃"
        }
    ]
}

就是每个地方的未来的七天的天气

import json
import pymongo
#建立连接
client = pymongo.MongoClient("mongodb://root:root@IP:端口")
#指定数据库
db = client['weather']
#指定集合
collection= db['weather_tian']
#指定要查询的内容
result= collection.find()
print('type result===',type(result))

fp = open('./output_weather.json','a+')
cal_index =0
for i in result:
    cal_index = cal_index +1
    if cal_index == 4:  #先打个三个地区出来看看情况
        break
    #print('type i =',type(i))
    i.pop('_id') #不如这个key和value不去掉的话，会报ObjectId错误的问题，因为这个是MongoDB里面的类，json不认识，你的自定定义这个类来处理
    j = json.dumps(i,ensure_ascii=False)
    fp.write(j)
    fp.write('\n') #这样每个地区的未来七天的天气情况就写为一行了

fp.close()

这样就在本地存了个json文件了。有三个地区的天气。

　　接下来我们是从这个json文件读入，变成dict，代码如下

import json
import time

def json_file_to_dict():
    ofile =  open('./output_weather.json')
    for  line in ofile.readlines():
        #print(line)
        print(type(line))
        afterjson = json.loads(line)
        print(afterjson['city']) #其中city是dict中的某个key

if __name__ == '__main__':
    json_file_to_dict()