On Fri, Feb 21, 2014 at 9:49 AM, Eli Bendersky <eli...@gmail.com> wrote:
> On Fri, Feb 21, 2014 at 6:46 AM, Nick Coghlan <ncogh...@gmail.com> wrote: > >> On 22 February 2014 00:37, Eli Bendersky <eli...@gmail.com> wrote: >> > This goes against anything I understand about how exceptions should and >> > should not be used. >> >> I think you're thinking of a language that isn't Python - we use >> exceptions for control flow all over the place (it's how hasattr() is >> *defined*, for example). >> > > No, it is Python I'm thinking about. As I mentioned in the reply to > Brett's message, I see a difference between allowing exceptions on > expression level and statement level. The latter is less likely to be > abused. Once you add exceptions into expressions, all bets are off. > > For instance, it is sometime non-trivial to know which exceptions some > function may throw. When you write a try...raise statement, you think hard > about covering all the bases. In an expression you're unlikely to, which > opens up a lot of possibilities for bugs. Again, please stop focusing just > on the list[index] case -- the proposal adds a new significant feature to > the language that can (and thus will) be used in a variety of scenarios. > I understand you are arguing that a try expression will lead to people just doing `something() except Exception: None` or whatever and that people will simply get lazy and not think about what they are doing with their exceptions. Unfortunately they already are; that shipped sailed when we didn't eliminate bare except clauses in Python 3 (hopefully we can change that in Python 4). I personally don't think that making people type out a try statement is going to lead to that much thought compared to an expression. I'm willing to bet most IDEs have a code snippet for creating a try statement so people are already not using the extra typing of a full-blown statement with at least two clauses as a way to stop and think about what they are doing. I'm totally fine restricting this proposal to not having any concept of exception catching or finally clause: it just replaces the simplest try/except clause possible (while requiring an exception be specified). That takes care of the common control flow use case of exceptions while requiring more thought for more complex cases.
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