在 For 循环中将键/值对附加到 Python 字典，输出排序答案

【问题标题】：Appending Key/Value Pairs to Python Dictionary in For Loop, Output Ordering在 For 循环中将键/值对附加到 Python 字典，输出排序
【发布时间】：2018-03-19 00:16:59
【问题描述】：

我正在尝试将用户名字段添加到输出列表中的 3 个字典中的每一个中，然后我想将每个字段作为键/值对作为字段#/字段值添加到其各自的字典中，以便轻松放置项目在 DynamoDB 中。但是，当我在输出列表中输出字典的结果时，我收到了乱序字段（请记住，每个对象都有数千个字段）。

   #Result stores a list of dicts with username key/value pair and a long list of fields
    result = [{ username: nasa , fields: [Nebula, Moon, Star, ...]},{ username: nationalgeographic, fields: [Grass, Tree, ...] },{ username: kingjames, fields[Basketball, Hardwood, Jersey, ...]}]

    for i in result:
        #For each dict in list
        num = 1
        item = {}
        item['username'] = i['username']
        for tag in i['fields']:
            label_string = 'label' + str(num)
            item[label_string] = tag
            num += 1
        output.append(item.copy())
        #Output should store 3 dicts with username, and labels with tags
    for user in output:
        for key, value in user.items():
            print(key, value)

预期输出：

username nasa
field1 Nebula
field2 Moon
field3 Star
.
.
.
username nationalgeographic
field1 Grass
field2 Tree
.
.
.
username kingjames
field1 Basketball
field2 Hardwood
field3 Jersey
.
.
.

实际输出

username nasa
field333 Black Hole
field282 Asteroid
field122 Mars
.
.
.
username nationalgeographic
field122 Moss
field3323 Bark
field212 Wood
.
.
.
username kingjames
field233 Shoe
field9331 Headband
field211 Mesh

【问题讨论】：

标签： python nosql amazon-dynamodb

【解决方案1】：

订单不是由 Python 中的 dict 维护的。如果您想按插入顺序保留密钥，可以使用OrderedDict

from collections import OrderedDict

你的代码会变成

#Result stores a list of dicts with username key/value pair and a long list of fields
result = [{ username: nasa , fields: [Nebula, Moon, Star, ...]},{ username: nationalgeographic, fields: [Grass, Tree, ...] },{ username: kingjames, fields[Basketball, Hardwood, Jersey, ...]}]

for i in result:
    #For each dict in list
    num = 1
    item = OrderedDict()
    item['username'] = i['username']
    for tag in i['fields']:
        label_string = 'label' + str(num)
        item[label_string] = tag
        num += 1
    output.append(item.copy())
    #Output should store 3 dicts with username, and labels with tags
for user in output:
    for key, value in user.items():
        print(key, value)

【讨论】：