What does above exception points to in exception info thrown?

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The simplest built-in exception as below:

>>> 1/0
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ZeroDivisionError: division by zero

Throw exception info ,then whole press is done.

Define function f1 and not to define myException:

def f1():
    try:
        print(1/0)
    except:
        raise myException('my exception')

Call f1():

>>> f1()
Traceback (most recent call last):
  File "<stdin>", line 3, in f1
ZeroDivisionError: division by zero

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<stdin>", line 5, in f1
NameError: name 'myException' is not defined

When the info

Traceback (most recent call last):
  File "<stdin>", line 3, in f1
ZeroDivisionError: division by zero

thrown out,exception of print(1/0) is handled as we have seen that in the beginning.
Why the statement in the middle line is During handling of the above exception, another exception occurred: ,instead of After handling of the above exception, another exception occurred:?
What is above exception in the statement During handling of the above exception?It points to try ... except structure in f1 ,instead of exception resulted by 1/0?
If above exception points to exception resulted by 1/0,then After handling of the above exception, another exception occurred is better to describe all the exceptions here!

  • 3

    Because within the except block, where you are supposedly handling a caught exception, you were producing another exception. Indicating that your exception handler is faulty.

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    ♦

  • What is above exception in the statement During handling of the above exception?It points to try ... except structure in f1 ,instead of exception resulted by 1/0?

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  • 1

    What makes you say that? Line 3 is the one with the 1/0 on it.

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  • Its normal to catch and convert exceptions like this. It doesn’t mean your exception handler is faulty. It just means that your module want’s to raise its own custom exceptions according to its own rules.

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  • 1

    @tdelaney That would be fine if you did raise MyException from e. Without the explicit from e, Python assumes the newly raised exception was a new error. As it indeed was in this case.

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    ♦

This is exception chaining as described in The raise Statement. You catch the ZeroDivisionError. When you raise MyException, python will automatically add the current exception to its __cause__ attribute.

That’s why you see both exceptions listed. The one you raised, and the one put in the __cause__ attribute. Python lets you customize the exception in several ways, particularly with a “from” exception. Generically, that’s

raise myException from OtherException

More specifically, to fully suppress the original exception and keep it out of the __cause__ attribute, raise from None:

raise myException from None

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