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

[Vaclav Petras]

On Thu, Jun 25, 2015 at 3:41 AM, Moritz Lennert <
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.

Vaclav
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.osgeo.org/pipermail/grass-user/attachments/20150625/8e880995/attachment.html>