Is there a way to reraise a nested exception both without adding another nesting level and without removing all causes?

Python Help
1

Consider the following two examples.

>>> try:
...     try:
...         raise Exception
...     except:
...         raise Exception
... except Exception as e:
...     raise Exception
...     
Traceback (most recent call last):
  File "<python-input-13>", line 3, in <module>
    raise Exception
Exception

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "<python-input-13>", line 5, in <module>
    raise Exception
Exception

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "<python-input-13>", line 7, in <module>
    raise Exception
Exception

>>> try:
...     try:
...         raise Exception
...     except:
...         raise Exception
... except Exception as e:
...     raise Exception from None
...     
Traceback (most recent call last):
  File "<python-input-14>", line 7, in <module>
    raise Exception from None
Exception

What I want, though, is an output like this:

Traceback (most recent call last):
  File "<python-input-13>", line 3, in <module>
    raise Exception
Exception

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "<python-input-13>", line 5, in <module>
    raise Exception
Exception

None of

  • raise Exception
  • raise Exception from None
  • raise Exception from e

work.

How can I do this?

2

Hmm. I’m a bit lost in your example. Rather than using Exception everywhere, can you raise three different exception types please? Then it’d be clear which ones you’re expecting to be chained together.

3

raise E raises a new exception E.

raise on its own in an except clause re-raises the caught exception.

try:
    try:
        raise Exception
    except:
        raise Exception
except Exception as e:
    raise
4

In general, there’s probably a better way to structure your code. But if you need to, you can raise Exception from e.__cause__ or raise Exception from e.__context__. (The former is set by raise … from, the latter is the exception that triggered the except block where e was raised.)

5 
>>> try:
...     try:
...         raise Exception("AAA")
...     except:
...         raise Exception("BBB")
... except:
...     raise Exception("CCC")
...     
Traceback (most recent call last):
  File "<python-input-1>", line 3, in <module>
    raise Exception("AAA")
Exception: AAA

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "<python-input-1>", line 5, in <module>
    raise Exception("BBB")
Exception: BBB

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "<python-input-1>", line 7, in <module>
    raise Exception("CCC")
Exception: CCC

but what I want is

Traceback (most recent call last):
  File "<python-input-1>", line 3, in <module>
    raise Exception("AAA")
Exception: AAA

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "<python-input-1>", line 7, in <module>
    raise Exception("CCC")
Exception: CCC
6

Replace raise Exception("BBB")with just raise.

7

the inner try-except is standing in for some code I don’t control