Question

当用户“帐号”已存在时，我正试图阻止json.dump写入我的JSON文件。

这是我的代码：

new_student = {"name": 'test2', "account_no": 1237}
account_no = 1346
with open("student.json", "r", encoding="utf-8") as f:
    data = json.load(f)
    for a in data["student_numbers"]:
        if not account_no == a["account_no"]:
            data["student_numbers"].append(new_student)
            with open("student.json", "w", encoding="utf-8") as f:
                json.dump(data, f)
            break

这也是我的JSON：

{"student_numbers": [{"account_no": 1345, "name": "test"}, {"account_no": 1346, "name": "test2"}, {"account_no": 1347, "name": "test3"}]}

我试过了if account_no not in a["account_no"]，但我收到了这个错误：

TypeError`TypeError：'int'类型的参数不可迭代

Answer 1

new_student = {"name": 'test2', "account_no": 1237}
with open("student.json", "r", encoding="utf-8") as f:
    data = json.load(f)
    existed_ids = {a['account_no'] for a in data["student_numbers"]}  # set of ids
    if new_student['account_no'] not in existed_ids:
        with open("student.json", "w", encoding="utf-8") as f:
            data['student_numbers'].append(new_student)
            json.dump(data, f)

Answer 2

您的检查失败，因为当您遍历student_numbers时，这些是返回的account_no，即：1345,1346和1347.所以您在第一次迭代中看到，您的条件是已经满足因为1346！= 1345，所以json.dump()被激活了。

您想要的是创建account_no列表并使用in运算符进行检查。您不需要遍历students_numbers。

new_student = {"name": 'test2', "account_no": 1237}
account_no = 1346
with open("student.json", "r", encoding="utf-8") as f:
    data = json.load(f)
    accounts = [a["account_no"] for a in data["student_numbers"]]
    if account_no not in accounts:
        data["student_numbers"].append(new_student)
        with open("student.json", "w", encoding="utf-8") as f:
            json.dump(data, f)

如何在用户存在时停止json.dump写入

2 个答案: