[Cython] Redundant Cython exception message strings

[Vitja Makarov]

2011/5/28 Robert Bradshaw <robertwb at math.washington.edu>:
> On Fri, May 27, 2011 at 3:32 PM, Stefan Behnel <stefan_ml at behnel.de> wrote:
>> Hi,
>>
>> I recently stumbled over a tradeoff question with AttributeError, and now
>> found the same situation for UnboundLocalError in Vitja's control flow
>> branch. So here it is.
>>
>> When we raise an exception several times in different parts of the code with
>> a message that only differs slightly each time (usually something like
>> "'NoneType' has no attribute X", or "local variable X referenced before
>> assignment"), we have three choices to handle this:
>>
>> 1) Optimise for speed: create a Python string object at module
>> initialisation time and call PyErr_SetObject(exc_type, msg_str_obj).
>>
>> 2) Current way: let CPython create the string object when raising the
>> exception and just call PyErr_SetString(exc_type, "complete message").
>>
>> 3) Trade speed for size and allow the C compiler to reduce the storage
>> redundancy: write only the message template and the names as C char*
>> constants by calling PyErr_Format(exc_type, "message template %s", "X").
>>
>> Assuming that exceptions should be exceptional, I'm leaning towards 3). This
>> would allow the C compiler to collapse multiple usages of the same C string
>> into one data constant, thus reducing a bit of redundancy in the shared
>> library size and the memory footprint. However, it would (slightly?) slow
>> down the exception raising due to the additional string formatting, even
>> when compared to the need to build a Python string object that it shares
>> with 2). While 1) would obviously be the fastest way to raise an exception
>> (no memory allocation, only refcounting), I think it's not worth it for
>> exceptions as it increases both the runtime memory overhead and the module
>> startup time.
>>
>> Thoughts?
>
> Any back-of-the-envelope calculations on how much the savings would
> be? I think I'm leaning towards 3 as well, certainly not option 1.
>

For UnboundLocalError and NameError I used 2) way:

https://github.com/vitek/cython/commit/1fe86b85d965753244cd09db38b1089b40f09a58

So maybe I should add functions like __Pyx_RaiseUnboundLocalError and
__Pyx_RaiseClosureNameError that will  use 3) way.
How do you like put_error_if_unbound CCodeWriter method is that right
place for it?

-- 
vitja.