使用Python和if语句解析JSON

Here is the JSON data I have:

这是我拥有的JSON数据:

{
  "response": {
    "status": {
      "version": "4.2",
      "code": 0,
      "message": "Success"
    },
    "artists": [
      {
        "name": "Taylor Swift",
        "foreign_ids": [
          {
            "catalog": "facebook",
            "foreign_id": "facebook:artist:19614945368"
          }
        ],
        "hotttnesss": 0.99956,
        "id": "ARS54I31187FB46721"
      },
      {
        "name": "Ed Sheeran",
        "foreign_ids": [
          {
            "catalog": "facebook",
            "foreign_id": "facebook:artist:9189674485"
          }
        ],
        "hotttnesss": 0.994265,
        "id": "ARSDWSZ122ECCB706A"
      },
      {
        "name": "Calvin Harris",
        "foreign_ids": [
          {
            "catalog": "facebook",
            "foreign_id": "facebook:artist:19366141168"
          }
        ],
        "hotttnesss": 0.990559,
        "id": "ARJRB241187FB556A3"
      },
      {
        "name": "Sam Smith",
        "foreign_ids": [
          {
            "catalog": "facebook",
            "foreign_id": "facebook:artist:313595788739120"
          }
        ],
        "hotttnesss": 0.988203,
        "id": "ARUZM8A11C8A41519C"
      },
      {
        "name": "Maroon 5",
        "foreign_ids": [
          {
            "catalog": "facebook",
            "foreign_id": "facebook:artist:5330548481"
          }
        ],
        "hotttnesss": 0.984929,
        "id": "ARF5M7Q1187FB501E8"
      },
      {
        "name": "Sia",
        "foreign_ids": [
          {
            "catalog": "facebook",
            "foreign_id": "facebook:artist:10959868407"
          }
        ],
        "hotttnesss": 0.983516,
        "id": "AR6ENUY1187B994158"
      },
      {
        "name": "David Guetta",
        "foreign_ids": [
          {
            "catalog": "facebook",
            "foreign_id": "facebook:artist:7619396355"
          }
        ],
        "hotttnesss": 0.982656,
        "id": "ARH2QI91187FB3788D"
      },
      {
        "name": "Ellie Goulding",
        "foreign_ids": [
          {
            "catalog": "facebook",
            "foreign_id": "facebook:artist:135027136641"
          }
        ],
        "hotttnesss": 0.981786,
        "id": "ARKTTJV12592CDA07F"
      },
      {
        "name": "Wiz Khalifa",
        "foreign_ids": [
          {
            "catalog": "facebook",
            "foreign_id": "facebook:artist:12138756141"
          }
        ],
        "hotttnesss": 0.978492,
        "id": "ARN0GFV1187FB508CC"
      },
      {
        "name": "Ariana Grande",
        "hotttnesss": 0.978074,
        "id": "AROHQCR13244CF7152"
      }
    ]
  }
}

I'm trying to parse "catalog" and "foreign_id". Here is my code:

我正在尝试解析“catalog”和“foreign_id”。这是我的代码:

for item in data['response']['artists']:
    for row in item['foreign_ids']:
        print row['catalog'], row['foreign_id']

The results are:

结果是:

facebook facebook:artist:19614945368
facebook facebook:artist:9189674485
facebook facebook:artist:19366141168
facebook facebook:artist:313595788739120
facebook facebook:artist:5330548481
facebook facebook:artist:10959868407
facebook facebook:artist:7619396355
facebook facebook:artist:135027136641
facebook facebook:artist:12138756141

KeyError
Traceback (most recent call last)
<ipython-input-224-cbc34d6d831e> in <module>()
      1 for item in data['response']['artists']:
----> 2     for row in item['foreign_ids']:
      3         print row['catalog'], row['foreign_id']

KeyError: 'foreign_ids'

I think I know why; the last data row does not have "foreign_ids". How would I include an if statement to help me avoid this error? For example, the code outputs "None" when there is no array value called "foreign_ids".

我想我知道为什么;最后一个数据行没有“foreign_ids”。我如何包含if语句来帮助我避免此错误?例如,当没有名为“foreign_ids”的数组值时,代码输出“None”。

4 个解决方案

#1

You have to check to see if that column exists before you attempt to iterate over it. This approach is known as "look before you leap". Here we're using get, since it will return None by default and not raise the KeyError.

在尝试迭代该列之前,您必须检查该列是否存在。这种方法被称为“在你跳跃之前看”。这里我们使用get,因为它默认会返回None而不会引发KeyError。

for item in data['response']['artists']:
    if item.get('foreign_ids'):
        for row in item['foreign_ids']:
            print row['catalog'], row['foreign_id']

Alternatively, you could employ a default value through get which supplies an empty list to iterate over instead.

或者,您可以使用默认值get,它提供一个空列表来代替迭代。

for item in data['response']['artists']:
    for row in item.get('foreign_ids', []):
        print row['catalog'], row['foreign_id']

In both cases, you have to check to see if that key exists. The code you have assumes that it's always present, which is definitely not the case.

在这两种情况下,您都必须检查该密钥是否存在。您所拥有的代码假定它始终存在,但绝对不是这样。

#2

Instead of an if statement (which is perfectly valid), you can use a try/except block:

您可以使用try / except块代替if语句(完全有效):

for item in data['response']['artists']:
    try:    
        for row in item['foreign_ids']:
            print row['catalog'], row['foreign_id']
    except KeyError as Ex:
        print "{} not found in {}".format(Ex,item)

This gives:

...
facebook facebook:artist:7619396355
facebook facebook:artist:135027136641
facebook facebook:artist:12138756141
'foreign_ids' not found in {'id': 'AROHQCR13244CF7152', 'name': 'Ariana Grande', 'hotttnesss': 0.978074}

which IMO is cleaner since it explicitly acknowledges the problem and acts on it. Instead of print, you can do an alternate action like a log.

哪个国际海事组织更清洁,因为它明确承认问题并采取行动。您可以执行日志等备用操作,而不是打印。

#3

You could check to see if the key is in that part of the JSON object by doing:

您可以通过执行以下操作来检查密钥是否在JSON对象的该部分中:

if 'somekey' in somPartOfTheJson:
    jsonObj = json.loads(jsonStr)

    for item in jsonObj['response']['artists']:
        if 'foreign_ids' in item:
            for row in item['foreign_ids']:
                if 'catalog' in row and 'foreign_id' in row:
                    print row['catalog'], row['foreign_id']

#4

if 'foreign_ids' not in item:
    continue
for row in item['foreign_ids']:
....

#1