[GRASS-dev] [GRASS-user] Error in pansharp tool: missing grass.script

[Moritz Lennert]

On 25/06/15 15:58, Vaclav Petras wrote:
>
> On Thu, Jun 25, 2015 at 3:41 AM, Moritz Lennert
> <mlennert at club.worldonline.be <mailto:mlennert at club.worldonline.be>> wrote:
>
>     On 24/06/15 15:09, Vaclav Petras wrote:
>
>         It seems like one. I think it might help, at least help to
>         debug, if you
>         replace "import grass.script as grass" by "import grass.script as
>         gscript" and "grass." by "gscript.". I think this change should
>         be done
>         anyway in all source code.
>
>
>     Could you explain your reasoning behind this ? IMHO, it should not
>     make any difference whether you use grass or gscript as the alias.
>
>
> Sure. First of all, this just look strange by default I believe:
>
> import aaa.bbb as aaa
>
> Why not
>
> import aaa.bbb
>
> or often appropriate
>
> import aaa.bbb as bbb
>
> or (my favorite)
>
> import aaa.bbb as ab
>
> or simple
>
> import aaa
>
> ?
>
> Alias shouldn't create confusion which I think it creates.
>
> After
>
> import grass.script as grass
>
> which of the following will work?
>
> from grass import run_commad
> from grass import pygrass
>
> The second line will work although in the following case it is the first
> line.
>
> grass.run_command
> grass.pygrass
>
> Sure, this is just how Python interprets the import statements, so if
> you know it, you are fine, but why should we make reading of the source
> code harder then necessary?
>
> The current situation leads to cases like:
>
>  >>> import grass.script as grass
>  >>> grass.run_command
> <function run_command at 0x7f185ed61500>
>
> Fine.
>
>  >>> grass.script.run_command
> Traceback (most recent call last):
>   File "<stdin>", line 1, in <module>
> AttributeError: 'module' object has no attribute 'script'
>
> OK. We haven't imported grass.script in the proper way, so let's do it.
>
>  >>> import grass.script
>  >>> grass.script.run_command
> <function run_command at 0x7f185ed61500>
>
> Works.
>
>  >>> grass.run_command
> Traceback (most recent call last):
>   File "<stdin>", line 1, in <module>
> AttributeError: 'module' object has no attribute 'run_command'
>
> Does not work anymore.
>
> I think that broadly used
>
> import grass.script as grass
>
> is just a legacy from the first version of Python API where
> "grass.script" was the only package and thus it was just `grass`. Then
> new (sub-)packages were introduced, probably "grass.lib" which forced
> the former `grass` to be renamed/moved to `grass.script`. To avoid
> changing all calls of functions from `grass.run_command` to something
> else, `grass.script` was imported with alias `grass`. This then spread
> into new and user code because the code is (or hopefully was) the only
> documentation. The unfortunate part is that this was some very first
> version of the API which was never released as stable (official
> introduction of Python API is 7.0.0, it was just experimental and
> internal in 6.4) but it influenced the common practice which I think is
> not the best practice. At least, this is how I understand it.
>
> I don't see a reason why to keep it when there is a better practice
> available. We should especially change it in GUI and parser's --script.
> I believe none of them are change of the API, so it can be done anytime.
> The code itself should be changed too, we are doing a lot of other
> non-crucial changes anyway. The benefit is better code as an example for
> users and easier maintenance because it is just more clear.
>
> Well, that's what I think.

Thanks for that detailed explanation. Although I don't feel as strongly 
about this as you seem to (probably because my scripts are never that 
complex), I understand your point and I agree that i) we should have a 
unified way of doing it and ii) using your gscript (or something 
similar) is probably better than the current grass.

Moritz