Question

我刚开始尝试使用python，现在我处于一种两难的境地。

我正在尝试从json文档打印，而我只是获取数组中的最后一个元素。

[{
    "FullMeasure": "1/2 cup", 
    "FullWeight": "", 
    "IngredientGridHeaders": null, 
    "IngredientID": 1142, 
    "IngredientName": "frozen corn", 
    "IngredientStep": 10, 
    "LanguageId": 0, 
    "PostPreparation": ", thawed, drained", 
    "PrePreparation": "", 
    "QuantityNum": 0, 
    "QuantityText": "1/2", 
    "QuantityUnit": "cup", 
    "RecipeIngredientID": 6291555, 
    "TrialMeasure": "", 
    "TrialWeight": ""
  }, 
  {
    "FullMeasure": "1/4 cup", 
    "FullWeight": "", 
    "IngredientGridHeaders": null, 
    "IngredientID": 1523, 
    "IngredientName": "red pepper", 
    "IngredientStep": 20, 
    "LanguageId": 0, 
    "PostPreparation": "s", 
    "PrePreparation": "chopped", 
    "QuantityNum": 0, 
    "QuantityText": "1/4", 
    "QuantityUnit": "cup", 
    "RecipeIngredientID": 6291554, 
    "TrialMeasure": "", 
    "TrialWeight": ""
  }, 
  {
    "FullMeasure": "2 Tbsp.", 
    "FullWeight": "", 
    "IngredientGridHeaders": null, 
    "IngredientID": 20197, 
    "IngredientName": "chopped green chiles", 
    "IngredientStep": 30, 
    "LanguageId": 0, 
    "PostPreparation": ", drained", 
    "PrePreparation": "canned ", 
    "QuantityNum": 2, 
    "QuantityText": "2", 
    "QuantityUnit": "Tbsp.", 
    "RecipeIngredientID": 6291552, 
    "TrialMeasure": "", 
    "TrialWeight": ""
  },
{
    "FullMeasure": "", 
    "FullWeight": "", 
    "IngredientGridHeaders": null, 
    "IngredientID": 19682, 
    "IngredientName": "KRAFT DELI DELUXE Process American Cheese Slice", 
    "IngredientStep": 80, 
    "LanguageId": 0, 
    "PostPreparation": "s", 
    "PrePreparation": "", 
    "QuantityNum": 4, 
    "QuantityText": "4", 
    "QuantityUnit": "", 
    "RecipeIngredientID": 6291558, 
    "TrialMeasure": "", 
    "TrialWeight": ""
  }
]

我想得到所有的构成ID，所以我写了这段小代码来抓住IngredientID

rec = recipes['Recipes'][0]['Ingredients']
        for records in rec:
            value = {
                        'Ingredient ID': records['IngredientID']
                    }

当我返回值时，我得到

{
  "Ingreient ID": 19682
}

我正在尝试获取每个元素的成分ID，而我似乎无法弄明白。任何指针都将受到赞赏。谢谢

Answer 1

你现在正在做的是你每次循环都重新定义value。您需要在循环之前定义value并将其分配给您可以添加的空列表。

value = {'Ingredient ID':[]}
for records in rec:
    value['Ingredient ID'].append(records['IngredientID'])

您还可以将值定义为如下列表：

value = []
for records in rec:
    value.append(records['IngredientID'])

Answer 2

你是overwriting循环内的值。因此，最终结果将是json中的last ingredient_id。请尝试将值添加到list：

myList = []

rec = recipes['Recipes'][0]['Ingredients']
        for records in rec:
            value = {
                        'Ingredient ID': records['IngredientID']
                    }
            myList.append(value)

myList将拥有所有成分

您甚至可以使用一行来执行此操作：

[r['IngredientID'] for r in rec]

这将列出['1142',1523,..]

Answer 3

您每次都在重新分配变量value。因此，你得到了最后一个元素。相反，你应该尝试

# Your code
value = []
for records in rec:
    value.append(records['IngredientID']);

# print value     # this will have all required IngredientID

Answer 4

您每次通过该循环替换该值。您应该添加该值，而不是。

首先将值创建为空列表（在循环之前），然后在循环的每次迭代中，追加到该列表：

value = []
rec = recipes['Recipes'][0]['Ingredients']
for records in rec:
    value.append({'Ingredient ID': records['IngredientID']})

然而，拥有一个字典列表，其中每个字典具有一个具有相同已知密钥的单个值，似乎有点无意义。根据您的要求，您可能想要这样做：

    value.append(rec)

或

    value.append(records['IngredientID'])

Answer 5

您当前实施的一个问题是，每次找到新的value时，ingredient ID的值都会被覆盖。如果您需要获取值列表，那么即使添加新值，您也必须确保保留所有旧值。

如果您使values列表然后使用追加，您将获得所需的所有值：

values = []
for records in rec:
    ingredient_id = records.get('IngredientID', None)
    if ingredient_id:
        values.append(ingredient_id)

最好使用dict.get()方法检索值，然后检查它是否存在;否则你可能会遇到例外情况。

Answer 6

如果您只想要ID，可以使用列表推导，如下所示：

ids = [records['IngredientID'] for records in recipes['Recipes'][0]['Ingredients']]

Answer 7

另一种方法，defaultdict

from collections import defaultdict
recipe_ids = defaultdict(list)
for records in rec:
    recipe_ids['recipe id'].append(records.get('IngredientID'))

Answer 8

如果您只想要IngredientID的列表，请使用[rec['IngredientID'] for rec in records]

records = [{
    "FullMeasure": "1/2 cup", 
    "FullWeight": "", 
    "IngredientGridHeaders": null, 
    "IngredientID": 1142, 
    "IngredientName": "frozen corn", 
    "IngredientStep": 10, 
    "LanguageId": 0, 
    "PostPreparation": ", thawed, drained", 
    "PrePreparation": "", 
    "QuantityNum": 0, 
    "QuantityText": "1/2", 
    "QuantityUnit": "cup", 
    "RecipeIngredientID": 6291555, 
    "TrialMeasure": "", 
    "TrialWeight": ""
  }, 
  {
    "FullMeasure": "1/4 cup", 
    "FullWeight": "", 
    "IngredientGridHeaders": null, 
    "IngredientID": 1523, 
    "IngredientName": "red pepper", 
    "IngredientStep": 20, 
    "LanguageId": 0, 
    "PostPreparation": "s", 
    "PrePreparation": "chopped", 
    "QuantityNum": 0, 
    "QuantityText": "1/4", 
    "QuantityUnit": "cup", 
    "RecipeIngredientID": 6291554, 
    "TrialMeasure": "", 
    "TrialWeight": ""
  }, 
  {
    "FullMeasure": "2 Tbsp.", 
    "FullWeight": "", 
    "IngredientGridHeaders": null, 
    "IngredientID": 20197, 
    "IngredientName": "chopped green chiles", 
    "IngredientStep": 30, 
    "LanguageId": 0, 
    "PostPreparation": ", drained", 
    "PrePreparation": "canned ", 
    "QuantityNum": 2, 
    "QuantityText": "2", 
    "QuantityUnit": "Tbsp.", 
    "RecipeIngredientID": 6291552, 
    "TrialMeasure": "", 
    "TrialWeight": ""
  },
{
    "FullMeasure": "", 
    "FullWeight": "", 
    "IngredientGridHeaders": null, 
    "IngredientID": 19682, 
    "IngredientName": "KRAFT DELI DELUXE Process American Cheese Slice", 
    "IngredientStep": 80, 
    "LanguageId": 0, 
    "PostPreparation": "s", 
    "PrePreparation": "", 
    "QuantityNum": 4, 
    "QuantityText": "4", 
    "QuantityUnit": "", 
    "RecipeIngredientID": 6291558, 
    "TrialMeasure": "", 
    "TrialWeight": ""
  }
]

[rec['IngredientID'] for rec in records]

输出：

[1142, 1523, 20197, 19682]

Answer 9

鉴于答案的数量，我认为嘿为什么不再一个。
如果您有复杂的表达式，您可能需要查看jmespath，xslt json，例如：

>>> import jmespath
>>> jmespath.search('Recipes[0].Ingredients[*].IngredientID', recipes)
[1142, 1523, 20197, 19682]

Python Json。只获取json数组中的最后一个元素

9 个答案: