Hi Simon,
> This post has two purposes: An advertisement for trac ticket #11342,
> and a technical question about a trick used in that ticket.
>
> First, the question.
>
> Usually, an error is raised with an error message. And thus, the cdef
> function sage.structure.parent.raise_attribute_error(P,name) first
> creates a nice message stating that P does not have the attribute of
> the given name.
>
> But the typical fate of an attribute error is being caught. Hence,
> normally, nobody will ever see the error message, and it is a waste of
> time to create it in the first place.
I had a very similar problem with the test suite error messages which sometimg
slowed sown the suite but several order of magnitude. I solved this issue in
#8742 by creating a class for lazy format string. I'm not sure this will solve
your problem but if it does, maybe it is not a good idea to duplicate a
feature.
> One of the tricks that I use in #11342 to generally speed up getattr
> of parents and elements is to introduce a new class
> AttributeErrorMessage. It simply stores the class of P and the given
> attribute name. Its string representation is the error message, and it
> will *only* be created when requested (hence, not during
> initialisation and not if the error is simply caught).
In my usecases, I had some error message containing some " %s "%(bla) where
the conversion from bla to its string representation take some time. So my
idea was to create a class LazyFormat inheriting from str to create an object
sur that the % operator is only evaluated when __repr__ is called. I still
create the instance of LazyFormat which take a little time. I'm not sure how
this fits your usecase.
Cheers,
Florent
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