Re: Bug: ob-python mangles multiline :var values [9.3.6 (release_9.3.6-397-ga089600)]

[Jack Kamm <jackkamm@gmail.com>]

Hi Matt --

> A heads up... I believe this changes the scope of the :var variables,
> since they previously were local to the main() function and now they are
> declared globally. After this change, some of my existing python source
> blocks (i.e., ones in which I attempt to assign a new value to a
> variable defined by :var) now generate the following error:
>
> Traceback (most recent call last):
>   File "<stdin>", line 223, in <module>
>   File "<stdin>", line 214, in main
> UnboundLocalError: local variable 'members' referenced before assignment

Thanks for noticing this and pointing it out. This was an oversight on
my end (I don't really use ":var" or non-session blocks).

Unfortunately, the fix for the original bug will have to be a bit more
complicated to avoid this error. I'll put it on my todo list, but if
anyone wants to have a crack at it, that would be very welcome.

We should also add a unit test for this regression so it doesn't happen
again.

> I hesitate to call this a bug, since it would be fine to think of
> everything within the source block as local and the header :var
> declarations as global.

I think it's fair to call this a bug. I think it would be inconvenient
to be unable to assign to these variables. Also, I did not intend to
break any existing code with this.

> And I suppose it would be worthwhile to ask: Is this change consistent
> with other org-babel modules? Is there a canonical way that org-babel
> handles scope?

IMO everything ought to be in the same scope, and the user shouldn't
have to think about the scope of the main() function that ob-python
wraps the body in. Especially since non-session blocks are evaluated
independently of other blocks, we really shouldn't have to think about
their scope.

I'm not sure if the Org manual provides any guidance here, but from a
quick check I didn't see anything about it.

Ideally I think everything should just be in global scope; however
ob-python needs to use a wrapper function for the "return" keyword.