Python csv到json列顺序

Question

基本的 Python csv 到 json 脚本在最终的 JSON 中混合列顺序。知道为什么吗？

test.csv

animal,age,count,legs
dogs,3,5,4
cats,6,4,4
birds,2,1,2

脚本

import csv
import json

csvfile = open('test.csv', 'r')
jsonfile = open('test.json', 'w')

reader = csv.DictReader( csvfile)

jsonfile.write('[')
for row in reader:
    json.dump(row, jsonfile)
    jsonfile.write(',\n')
jsonfile.write(']')

test.json

[{"count": "5", "age": "3", "legs": "4", "animal": "dogs"},
{"count": "4", "age": "6", "legs": "4", "animal": "cats"},
{"count": "1", "age": "2", "legs": "2", "animal": "birds"},
]

Answer 1

因为字典没有任何顺序感，所以期望字典是任意顺序的。

如果您必须保留顺序（理想情况下您不应该这样做），您需要使用简单的 csv 阅读器读取每一行，然后创建 collection.OrderedDict 对象，这些对象确实存储了添加键的顺序.示例 -

from collections import OrderedDict
import csv
with open('test.csv','r') as f:
    reader = csv.reader(f)
    headerlist = next(reader)
    csvlist = []
    for row in reader:
            d = OrderedDict()
            for i, x in enumerate(row):
                    d[headerlist[i]] = x
            csvlist.append(d)

import json
with open('test.json','w') as f:
    json.dump(csvlist,f)

请注意，如果使用此 JSON 的解析器不以同样的方式尊重顺序，这仍然是无用的。

---

示例/演示 -

以我的test.csv 为-

animal,age,count,legs
dogs,3,5,4
cats,6,4,4
birds,2,1,2

test.json 看起来像 -

[{"animal": "dogs", "age": "3", "count": "5", "legs": "4"}, 
{"animal": "cats", "age": "6", "count": "4", "legs": "4"}, 
{"animal": "birds", "age": "2", "count": "1", "legs": "2"}]

Answer 2

在 Anand 的回答中，您只是暂时解决了问题。 JSON 文件可能以正确的顺序输出，但是您可以在另一个位置（例如浏览器或另一个 Python 进程）读取此数据，并且当它在此文件中读取时，将不会保留顺序！

如果您想保证数据源和目标之间的顺序，您将需要使用列表列表。

您可以执行以下操作来保持顺序：

import csv 
import json

lst = []
csvfile = open('test.csv', 'r')
jsonfile = open('test.json', 'w')
first_line = next(csvfile).split(',')

csvfile.seek(0) # we peeked at the first_line, lets reset back to beginning

reader = csv.DictReader(csvfile)

for row in reader:
    group = []
    for h in first_line:
        h = h.strip()
        group.append([h, row[h]])
    lst.append(group)

jsonfile.write(json.dumps(lst))

输出：

[[["animal", "dogs"], ["age", "3"], ["count", "5"], ["legs", "4"]], [["animal", "cats"], ["age", "6"], ["count", "4"], ["legs", "4"]], [["animal", "birds"], ["age", "2"], ["count", "1"], ["legs", "2"]]]