How do you raise a custom exception?

Question

BlackTom AI · Accepted Answer

Use the raise keyword together with an Exception instance: raise Exception("error").

Relevant concepts:
- In Python, exceptions are objects (instances of Exception or its subclasses).
- The raise statement signals that an exception should be thrown; the interpreter then unwinds the stack until a matching except block handles it.
- You can raise built-in exceptions (Exception("msg")) or your own by subclassing Exception and raising an instance of that subclass.

Step-by-step reasoning and example:
1. Construct an exception object: Exception("error") creates an Exception instance whose message is "error".
2. Use raise to throw that exception: raise Exception("error"). The interpreter immediately stops normal execution in the current block and begins exception propagation.
3. A try/except block can catch it:
   try:
       raise Exception("error")
   except Exception as e:
       print("Caught:", e)
   This prints "Caught: error".

If you want a truly custom exception class, define it and raise an instance:
   class MyError(Exception):
       pass
   raise MyError("custom message")
This follows the same pattern (raise <ExceptionInstance>).

Why the correct answer is raise Exception("error"):
- It uses the raise keyword (required to throw an exception) and provides an Exception instance (required to specify what to raise).
- It is valid Python syntax and produces the intended behavior (an exception is raised and can be caught).

Why the other options are incorrect:
- custom Exception("error"): "custom" is not a Python keyword or operation; this is invalid syntax.
- error.raise(): This suggests calling a raise method on an object named error; no such standard method exists and this does not raise an exception.
- create Exception("error"): "create" is not a Python keyword; this is invalid syntax and does not raise.

Conclusion: The correct way shown in the options is raise Exception("error"), which matches the provided answer.

How do you raise a custom exception?单项选择题

类似问题

Pick the code/s that correctly implements the following: Get a user input and save as 'min' variable if this input is not an integer, go to step 1 print it out to the console and exit the loop

Which keyword handles a thrown exception?

Which keyword explicitly throws an exception?

Error handler codes, to handle unusual errors are:

What does the finally block do?

For the following code: What will the value be for istr after this code executes?

What happens when a raise statement is encountered in a function?

What happens if an exception occurs and there is no matching catch block, but a finally block exists?

更多留学生实用工具

智能学习助手

风格化写作助手

论文查重助手

文献引用助手

课堂转译助手

课堂笔记助手

Quiz搜索助手

学校历年真题

智能刷题助手

智能匹配练习

希望你的学习变得更简单