On Feb 23, 2014 7:52 PM, "Stefan Behnel" <stefan...@behnel.de> wrote: > > Chris Angelico, 21.02.2014 04:15: > > Just as PEP 308 introduced a means of value-based conditions in an > > expression, this system allows exception-based conditions to be used > > as part of an expression. > > [...] > > This currently works:: > > > > lst = [1, 2, None, 3] > > value = lst[2] or "No value" > > > > The proposal adds this:: > > > > lst = [1, 2] > > value = lst[2] except IndexError: "No value" > > I see a risk of interfering with in-place assignment operators, e.g. > > x /= y except ZeroDivisionError: 1 > > might not do what one could expect, because (as I assume) it would behave > differently from > > x = x / y except ZeroDivisionError: 1
Yes. Augmented assignment is still assignment, so a statement. The only way to parse that is as x /= (y except ZeroDivisionError: 1) and it'd be equivalent to x = x / (y except ZeroDivisionError: 1) (If the parentheses are mandatory that makes it easier to spot the difference.) > > I think that falls under the "overly broad exception handling" issue. If > you want to include the assignment, you'll have to spell out the try-except > block yourself. I find the difference in the two behaviours very > unfortunate, though. > > This also reduces the scope of applicability somewhat. Cython has typed > assignments, so a straight forward idea would be to handle TypeErrors in > assignments like this: > > cdef str s > s = x except TypeError: str(x) > > However, I guess that would similarly counter the idea of exception > handling in an *expression*, and the correct and non-ambiguous way to do > this would be to spell out the try-except block. > > Summing it up, my impression is that it helps some use cases but leaves > others more ambiguous/unclear/unfortunate, which makes me lean towards > rejecting it. > > Stefan > > > _______________________________________________ > Python-Dev mailing list > Python-Dev@python.org > https://mail.python.org/mailman/listinfo/python-dev > Unsubscribe: https://mail.python.org/mailman/options/python-dev/thomas%40python.org
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