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引发自定义异常类

定义可映射为 JSON 的领域错误

引发自定义异常类 是 CoddyKit 上的免费 Flask Academy 课时。这是第 3 节课，共 4 节。你可以在下方免费阅读本课时的完整内容 — 然后在浏览器中使用内置代码编辑器和全天候 AI 导师进行实践。这是 Flask Academy 学习路径的一部分，你的进度在网页和 CoddyKit 应用中同步。 Flask Academy 课程共包含 4 节课。

本课时的部分内容尚未翻译，以英文显示。

Errors That Speak Your Domain

Numbers like 400 are generic. A custom exception names the real problem, such as a payment that failed or a quota hit.

Subclass an Exception

You start by defining a class that inherits from Exception. This gives you a clear, raisable error of your own.

class PaymentError(Exception):
    pass

Add a Status Code

Give the class a status_code attribute so a handler knows which HTTP code to send when it fires.

class PaymentError(Exception):
    status_code = 402

Carry a Message

Store a human message in the constructor. Your handler can later read it and place it into the response body.

def __init__(self, message):
    self.message = message

Raise It in a View

Inside a view you simply raise the error when something goes wrong. Flask then looks for a matching handler.

if not paid:
    raise PaymentError("Card declined")

Handle the Custom Class

@app.errorhandler(PaymentError)
def on_pay(e):
    return e.message, e.status_code

Return JSON From It

For an API, turn the error into JSON inside the handler. Clients get a structured failure they can parse reliably.

return jsonify(error=e.message), e.status_code

One Base for Many Errors

Make a single base class and let specific errors subclass it. Then one handler can cover your whole error family.

class ApiError(Exception):
    pass

Default Sensible Values

Give the base a default status_code like 400. Subclasses override it only when they need a different one.

class ApiError(Exception):
    status_code = 400

Keep Logic Out of Views

Raising domain errors lets views stay short. The handler owns formatting, so each view just signals what went wrong.

Why This Scales

As an app grows, custom exceptions keep error logic in one tidy spot. New error types plug into the same clean pipeline.

Quick Check

How does a view trigger your domain error?

Recap

You built custom exception classes with a status code and message, raised them in views, and mapped them to clean JSON. Awesome!

常见问题解答

「引发自定义异常类」课时是免费的吗？

是的 — 「引发自定义异常类」的完整文本可在网页上免费阅读。要进行交互式练习（内置代码编辑器和全天候 AI 导师）并解锁 Flask Academy 课程的其余内容，请升级到 CoddyKit PRO。 Flask Academy 课程共包含 4 节课。

「引发自定义异常类」这节课中我会学到什么？

定义可映射为 JSON 的领域错误你通过在浏览器中直接运行的动手代码来练习 Flask Academy，全天候 AI 导师会在你学习这节课的过程中回答你的问题。

学习 Flask Academy 需要有经验吗？

无需任何先前经验。CoddyKit 上的 Flask Academy 课程适合初学者到高级学习者，你可以从这里开始或从头开始，按照自己的节奏学习。这是第 3 节课，共 4 节。

「引发自定义异常类」课时需要多长时间？

大多数 CoddyKit 课程大约需要 5–10 分钟。每节课都很精短且互动，所以你能稳步进步，并在网页和应用中从离开的地方继续。

我能在这节 Flask Academy 课中编写并运行代码吗？

能。每节 Flask Academy 课都包含内置代码编辑器，你可以在浏览器中直接编写并运行真实代码，并获得即时 AI 反馈 — 无需本地设置。

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