On 4/8/21 1:21 PM, Chris Angelico wrote:
On Fri, Apr 9, 2021 at 6:16 AM Ethan Furman wrote:
On 4/8/21 11:25 AM, Chris Angelico wrote:
Similar question: What would be the semantics of this?
with contextlib.suppress(BaseException):
a = b / c
except BaseException as e:
print(e)
What types of exception could be caught and what types couldn't?
Well, if every exception is derived from BaseException (they are) and
contextlib.suppress(BaseException) suppresses all
BaseException-derived exceptions (it does) then the semantics of the above are:
- "a" will be the result of "b / c" if no exception occurs
- otherwise, "a" will be whatever it was before the with-block
- no exception will ever be caught by the except-clause
Generally speaking, no exception that a context manager handles (i.e.
suppresses) will ever be available to be caught.
What about NameError looking up contextlib, or AttributeError looking
up suppress? Will they be caught by that except clause, or not?
Ah, good point -- those two would get caught, as they happen before
contextlib.suppress() gets control.
Thank you for making my point: your assumption is completely the
opposite of the OP's, given the same syntactic structure.
The guidance should be: `try with` behaves exactly as `try/except with a with`, meaning that NameError and
AttributeError for those two reasons would still be caught. Yes, it's easy to miss that at first glance, but it's just
as easy to miss in the traditional try/except layout:
```python
try:
with contextlib.suppress(BaseException):
# do stuff
except BaseException as e:
print(e)
```
How many people are going to look at that and think, "oh, NameError and
AttributeError can still be caught" ?
--
~Ethan~
_______________________________________________
Python-ideas mailing list -- python-ideas@python.org
To unsubscribe send an email to python-ideas-le...@python.org
https://mail.python.org/mailman3/lists/python-ideas.python.org/
Message archived at
https://mail.python.org/archives/list/python-ideas@python.org/message/KANA7OVE4VLYZWWDCRTCO6F6GQDZ3XZ2/
Code of Conduct: http://python.org/psf/codeofconduct/
