python - 如果 json 键不存在则跳过

Question

我正在运行以下命令:

for server in server_list:
    for item in required_fields:
        print item, eval(item)

某些 key 可能不存在，但更糟糕的是，它显示在父 key 上，而不是我正在扫描的 key 上。

所以我正在扫描 json 中的以下键:

server['server_management']['server_total_cost_of_ownership']['description']

它不存在，但实际上是 null 的父级:

server['server_management']['server_total_cost_of_ownership']

我该如何编写代码来解决这个问题？它没有给出关键错误。现在我得到以下回溯:

Traceback (most recent call last):
  File "C:/projects/blah/scripts/test.py", line 29, in <module>
    print item, eval(item)
  File "<string>", line 1, in <module>
TypeError: 'NoneType' object has no attribute '__getitem__'

完整代码:

import csv
import json
import os
import requests
import sys

required_fields = ["server['server_name']","server['server_info']['asset_type']['display_name']",
                   "server['asset_status']['display_name']", "server['record_owner']['group_name']",
                   "server['server_management']['server_total_cost_of_ownership']['description']",
                   "server['server_management']['primary_business_owner']['name']",
                   "server['environment']['display_name']", "server['is_virtual']",
                   "server['managed_by']['display_name']", "server['server_info']['billable_ibm']",
                   "server['server_info']['billing_sub_type']['display_name']",
                   "server['server_info']['serial_number']", "server['location']['display_name']",
                   "server['inception_date']", "server['server_info']['decommission_date']" ]

# Query API for all servers
def get_servers_info():
    servers_info = requests.get('url')
    return servers_info.json()

def get_server_info(sid):
    server_info = requests.get('url')
    return server_info.json()

server_list = get_servers_info()
for server in server_list:
    for item in required_fields:
        print item, eval(item)

Answer 1

事实上你应该避免 eval。 json 加载后，由于您知道键名称，因此可以使用列表深入树中。

server['server_management']['primary_business_owner']['name']" => ["server_management', 'primary_business_owner', 'name']

这里是针对必填字段列表进行 json 验证的片段。

data={
    "d": {
        "p":{
            "r":[
                "test"
            ]
        }
    },
    "a": 3
}


def _get_attr(dict_, attrs):
    try:
        src = attrs[:]
        root = attrs.pop(0)
        node = dict_[root]
        null = object()
        for i, attr in enumerate(attrs[:]):
            try:
                node = node.get(attr, null)
            except AttributeError:
                node = null
            if node is null:
                # i+2 pop and last element
                raise ValueError("%s not present (level %s)" % (attr, '->'.join(src[: i+2])))
        return node
    except KeyError:
        raise ValueError("%s not present" % root)

# assume list of required field
reqs = [
    ["d", "p", "r"],
    ["d"],
    ["k"],
    ["d", "p", "r", "e"],
]

for req in reqs:
    try:
        _get_attr(data, req)
    except ValueError as E:
        print(E)
# prints
# k not present
# e not present (level d->p->r->e)