python - 使用 Python 和 if 语句解析 JSON

Question

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"
      }
    ]
  }
}

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']

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'

我想我知道为什么；最后一个数据行没有“foreign_ids”。我将如何包含 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”。

Answer 1

在尝试迭代之前，您必须检查该列是否存在。这种方法被称为“三思而后行”。这里我们使用 get，因为默认情况下它会返回 None 并且不会引发 KeyError。

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

或者，您可以通过 get 使用默认值，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']

在这两种情况下，您都必须检查该 key 是否存在。您拥有的代码假定它始终存在，但事实并非如此。