Re: [pygccxml-development] Patch to add a little syntactic sugar

[Allen B. <al...@vr...>]

Roman Yakovenko wrote:

> On 5/17/06, Roman Yakovenko <rom...@gm...> wrote:
>
>> On 5/17/06, Allen Bierbaum <al...@vr...> wrote:
>> > I have included a patch that I find useful for simplifying decl lookup
>> > in pyplusplus.
>> >
>> > It allows code like the following to be written using the __getitem__
>> > interface.
>> >
>> > ns = mb.global_ns.namespace( 'my_ns',)
>> > ns["MyClass"].exclude()
>> > class_a = ns["ClassA"]
>> > class_a["doSomething"].include()
>
>
> I like this part of the patch
>
>> > It also allows an attribute interface (similar to Pyste).
>> >
>> > ns.MyClass.exclude()
>> > class_a = ns.ClassA
>> > class_a.doSomething.include()
>
>
> This one I like less. If user made some mistake and spelled wrong 
> property name
> of the class_t or namespace_t and there is a declaration with that name,
> then .... I prefer to apply the patch without __getattr__ part.
>
> Thoughts?

I assume you mean something like:

MyClass.someMethod.call_policies = ....

so what if they spell it 'call_pooicies', it that case it will raise the 
exception that python would normal raise and just throw and AttributeError.

In the case of trying to look up a decl and spelling that decl wrong, 
for example:

MyClass.someMethod_bad

it still throws an AttributeError because that is the standard way to 
deal with a python attribute lookup problem.  It would be nice if the 
exception included the name that failed, but I don't see a way to do this.

I thought about just allowing a failed find to throw the pyplusplus 
RuntimeError exception for a failed lookup, but this would make all the 
decl classes behave dramatically different then they way python would 
expect them to work normally.  For example in a previous e-mail I talk 
about how there are some failed attemtps to look up '__newstate__'.  The 
code that is failing with this lookups is able to work correctly (I 
would guess) because it catches the AttributeError exception to detect 
that the lookup failed.  If we changed it so the classes didn't throw 
this exception anymore, this code would fail because it would not be 
expecting a RuntimeError.

So, it is not a perfect solution, but it seems like a reasonable one 
since it makes the attribute lookup keep behaving as standard python 
lookups would.

-Allen