Re: [pypy-dev] DLS paper on RPython
[I respond only to you because I don't think Massimo and Davide are interested in such details; I'm also cc-ing pypy-dev] Niko Matsakis wrote:
Ok. I'll look at that some. I may have to rewrite my section on exceptions to describe the type-wrapping solution; I wrote it to describe the newer system I started to checked in today, but then I found that RPython allows any object, not just Exceptions, to be thrown, meaning that this newer system won't work as well as I thought (and so is currently disabled).
Probably the simplest way to solve the problem is not to allow arbitrary objects to be thrown in RPython; I quick grep inside objspace/std and interpret didn't show any case in which this feature is used, and in any case it should be very easy to patch. Else, you could special-case the raise/except when using subclasses of Exception, and don't do the wrapping in those cases; of course you would have to be careful when catching all the exceptions, something like this: try: foo() except: bar() needs to be translated to: try { foo() } catch(Exception e) { // this is __builtin__.Exception bar() } catch(ExceptionWrapper e) { bar() } or something similar. I think we should really try to avoid ExceptionWrapper beacuse it's both ugly and probably veeery slow. ciao Anto
I guess the question is whether people consider the ability to throw arbitrary objects (rather than only those whose type is a subtype of Exception) a feature or a bug. I'm on the fence myself: it makes translating to the jvm and clr easier if we prohibit arbitrary objects, and it seems like a marginal use-case, but on the other hand, well, Python can do it, so why not? If anyone wanted to give me a few pointers as to what has to be changed to force exceptions to be subtypes of Exception, I'd be excited to try hacking it, just so I can learn more about that part of PyPy. On the other hand, I think that a hybrid wrapping strategy could actually work reasonably well and avoid wrapping in the 99% of cases where Exception sub-types are thrown and caught. Therefore, I'd say the real question is how people on the list think that RPython "ought" to behave. Niko
Niko Matsakis wrote:
I guess the question is whether people consider the ability to throw arbitrary objects (rather than only those whose type is a subtype of Exception) a feature or a bug.
I'm on the fence myself: it makes translating to the jvm and clr easier if we prohibit arbitrary objects, and it seems like a marginal use-case, but on the other hand, well, Python can do it, so why not?
the idea is that only subclasses of Exception/BaseException can be thrown in RPython, we have no code to enforce that right now OTOH if you find places in our RPython code that don't do that those are bugs to fix.
If anyone wanted to give me a few pointers as to what has to be changed to force exceptions to be subtypes of Exception, I'd be excited to try hacking it, just so I can learn more about that part of PyPy.
On the other hand, I think that a hybrid wrapping strategy could actually work reasonably well and avoid wrapping in the 99% of cases where Exception sub-types are thrown and caught.
Therefore, I'd say the real question is how people on the list think that RPython "ought" to behave.
Niko
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the idea is that only subclasses of Exception/BaseException can be thrown in RPython, we have no code to enforce that right now OTOH if you find places in our RPython code that don't do that those are bugs to fix.
Okay, I guess the right thing to do then is to insert a CHECKCAST when the static type of a thrown exception is not a sub-type of Exception. "Correct" RPython should work, and the rest will throw a ClassCastException. If the annotator/rtyper were later changed to provide a static type better than Object, then the casts won't be generated. That's what I've done for now. It fixes the broken test, at least. :) Niko
"Niko Matsakis"
participants (4)
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Antonio Cuni -
Niko Matsakis -
Samuele Pedroni -
Terry Reedy