如何在Robot Framework中获取JSON数组长度？遇KeyError报错

问题场景 #

执行以下Robot Framework代码时，第一行解析JSON正常，但获取数组长度时触发KeyError：

${json_object}    evaluate        json.loads('''${sn_booking_payload}''' , strict=False)    json
${answers_count}    Get Length    ${json_object["$.preBookAnswers.answers[0]"]}

报错信息：

Resolving variable '${json_object["$.preBookAnswers.answers[0]"]}' failed: KeyError: '$.preBookAnswers.answers[0]'

目标JSON片段（需获取preBookAnswers下answers数组的长度）：

"preBookAnswers": {
    "answers": [
                    {
                        "entityId": "2bfd67b0-a315-4dd1-b3e1-ce1d417e9cf9",
                        "userInput": "",
                        "itemIds": [],
                        "answers": [
                            {
                                "item": "Customer Meeting",
                                "value": "",
                                "description": ""
                            }
                        ],
                        "customFieldType": "QUESTION",
                        "questionDisplayText": "Reason for Travel"
                    },
                    {
                        "entityId": "ec376e47-b7d7-47f5-811d-90430eae02f8",
                        "userInput": "",
                        "itemIds": [],
                        "answers": [
                            {
                                "item": "J123",
                                "value": "",
                                "description": ""
                            }
                        ],
                        "customFieldType": "QUESTION",
                        "questionDisplayText": "DP Code"
                    }
    ],
    "preBookQuestionResponseId": ""
}

错误原因 #

json.loads解析后得到的${json_object}是Python字典对象，不支持JSONPath语法（$.preBookAnswers.answers[0]是JSONPath写法）。代码中把JSONPath字符串当成字典的key去访问，自然会触发KeyError。

修正方案 #

直接用Python字典的嵌套访问语法，逐层获取目标数组后再取长度：

方案1：分步获取 #

${json_object}    evaluate        json.loads('''${sn_booking_payload}''' , strict=False)    json
# 先取出answers数组
${answers_array}    evaluate    ${json_object["preBookAnswers"]["answers"]}
# 再获取数组长度
${answers_count}    Get Length    ${answers_array}

方案2：直接链式访问 #

${json_object}    evaluate        json.loads('''${sn_booking_payload}''' , strict=False)    json
${answers_count}    Get Length    ${json_object["preBookAnswers"]["answers"]}

两种方式都能正确拿到answers数组的长度（示例中为2）。

内容的提问来源于stack exchange，提问作者Christian Dayao Corp