Question

初学者问题。

我正在卷曲我的数据库以查看特定requestId是否存在某个对象。

理想情况下，我的代码类似于：

if totalobjects_start == 0:
    create a cron job
elif totalobjects_start < 24:
    pass

当表中存在带有该requestId的1+对象时，这很好。请注意，该属性totalObjects为1。

{"offset":0,"data":[{"created":1439328152000,"locationId":0,"requestId":"A6NMD6","latency":0,"___class":"Latency","totalObjects":1}

但是，如果表中没有requestId的对象，则JSON转储如下所示：

{"code":1017,"message":"Invalid where clause. Not existing columns: "}

我遇到的问题是为条件语句分配变量的内容。如果表中没有对象，并且我尝试将totalobjects_start分配给JSON属性totalObjects，我将获得KeyError，因为它不存在于JSON转储中

这是我想要做的伪代码：

try to see if code 1017
if not, see if totalObjects is at least 1

if code 1017 (no objects):
    create a cron job
elif totalObjects is at least 1 and less than 24:
    pass

以下代码显然是错误的，但我想至少付出努力：

totalobjects_start_str = totalobjects_search_start.decode(encoding='utf-8')

def totalobjects_count():
    try:
        totalobjects_start_1017 = json.loads(totalobjects_start_str, strict=False)['code']
    except (ValueError, KeyError, TypeError):
        totalobjects_start = int(json.loads(totalobjects_start_str, strict=False)['totalObjects'])

totalobjects_count()

if totalobjects_start_1017 == '1017':
    job.hours.every(2)
    cron.write()
elif totalobjects_start < 24:
    pass

Answer 1

通常使用in关键字来检查dict中是否存在密钥。如果您还不知道这一点 - 当您在python中加载json字符串时，它会将其转换为dict。在下面的代码中，假设响应变量实际上由db驱动程序填充。

import json

# Pretend the following came from the db
response = '{"code":1017,"message":"Invalid where clause. Not existing columns: "}'
data = json.loads(response)
if 'code' in data and data['code'] == 1017:
    # create the cron
elif 'totalObjects' in data and 0 < data['totalObjects'] < 24:
    # probably log this somewhere
    pass
else:
    # probably have some action for when totalObjects is 0 or >= 24
    pass

Answer 2

我对crontab不太了解，但你的代码部分似乎非常正确。我认为这可以帮助您解决JSON数据的问题。

import json

data1 = json.dumps({'a':123, 'b':456, 'requestId': 329864798}) #sample json data with 'requestId'
data2 = json.dumps({'a':123, 'b':456}) #sample json data without 'requestId'

def totalobjects_count(data):
    d = json.loads(data)
    try:
        if d['requestId']:
            return 1
    except KeyError:
        return 1017

totalobjects = totalobjects_count(data1) #use data1 and data2 alternatively to simulate both use-cases

if totalobjects == 1:
    #do something here
    pass
elif totalobjects == 1017:
    #show some error or execute alternative code
    pass
else:
    pass

解析JSON时处理KeyError

2 个答案: