Exception chaining

I would like to be able to have sentry display the original exception in the chain. In a lot of places we do something like this:

try:
    v = {}['a']
except KeyError as e:
    raise ValueError('failed') from e

I would like to be able to get at the KeyError in sentry just like the output of python when this code is ran:

Traceback (most recent call last):
  File "t.py", line 2, in <module>
    v = {}['a']
KeyError: 'a'

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "t.py", line 4, in <module>
    raise ValueError('failed') from e
ValueError: failed

Is this possible in raven?

[kiwiholmberg]

Would very much like this functionality!

[cjerdonek]

I haven’t noticed any issues with Sentry’s aggregation of chained exceptions.

@phillbaker This is what you should be doing to take advantage of the client’s support for chaining:

try:
    requests.get("http://example.com")
except requests.exceptions.ConnectionError:
     raise MylibError("Unable to connect")

That way Python chains the ConnectionError to MylibError (and Sentry will render it), and Sentry will aggregate only on the info of what you pass to MylibError’s constructor.

Doing raise MylibError("Unable to connect", e) from None breaks this because (1) including from None breaks the chain (and so losing information from Sentry’s rendering), and (2) it includes the ConnectionError object in the constructor, which I could see causing Sentry not to aggregate different MylibError objects.