[GRASS-dev] grass.info versus print

[Paulo van Breugel]

On 14-04-16 14:27, Vaclav Petras wrote:
>
> On Thu, Apr 14, 2016 at 7:33 AM, Paulo van Breugel 
> <p.vanbreugel at gmail.com <mailto:p.vanbreugel at gmail.com>> wrote:
>
>     On Thu, Apr 14, 2016 at 1:04 PM, Glynn Clements
>     <glynn at gclements.plus.com <mailto:glynn at gclements.plus.com>> wrote:
>
>
>         In general, scripts should use the g.message wrappers rather than
>         Python's "print" statement or os.write(), as that will honour any
>         configuration options (GRASS_VERBOSE, GRASS_MESSAGE_FORMAT,
>         --quiet/--verbose, etc).
>
>
>     Thanks Glynn. It seems there are different opinions, see earlier
>     comment from Vaclav.
>
>
> Perhaps I was not completely clear before. I agree with Glynn. 
> grass.script.message() etc. for messages. print()/sys.stdout for text 
> output (e.g. tables).
>
>     Also in the examples on the Wiki (e.g., on
>     https://grasswiki.osgeo.org/wiki/GRASS_and_Python) and various
>     addons I have looked at, I can see both being used.
>
>
> I would have to go through the individual examples but sometimes it 
> might be be clear what is a message to inform user about something and 
> what is a text output of the module. A rule of thumb can be that 
> modules which output maps, (usually) don't do text output, so they 
> shouldn't use print().

In this case (r.vif) the output is not a map, but a list of values, 
i.e., text output (see below). Based on the guidelines, I would assume I 
should use print()?

All variables

----------------------------------------

variable                           vif      sqrtvif

2000_01_precip at climate_1970_2012       2.30     1.52

2000_03_tempmean at climate_1970_2012    24.95     5.00

2000_11_precip at climate_1970_2012       3.54     1.88

2001_02_precip at climate_1970_2012       4.55     2.13

2001_04_tempmean at climate_1970_2012    25.01     5.00

Variable '2001_04_tempmean at climate_1970_2012' removed

----------------------------------------

variable                           vif      sqrtvif

2000_01_precip at climate_1970_2012       2.30     1.52

2000_03_tempmean at climate_1970_2012     2.19     1.48

2000_11_precip at climate_1970_2012       3.48     1.87

2001_02_precip at climate_1970_2012       4.54     2.13

Final selected variables are: 2000_01_precip, 2000_03_tempmean, 2000_11_precip, 2001_02_precip

with as maximum VIF: 5.69787583189



>
> Also for you personal scripts, you are free to use any solution you 
> want. That might be what the examples are showing. However, Python 
> scripts which are modules, for example in Addons, should adhere to the 
> submitting guidelines:
>
> https://trac.osgeo.org/grass/wiki/Submitting/Python#Messages
>
>     Perhaps the most important thing is that one should avoid mixing
>     the two, which is something that maybe could go somewhere in the wiki?
>
>
> Feel free to extent either wiki or guidelines if you think it is not 
> clear enough.

I wouldn't mind doing so, but I probably should understand better myself 
what exactly the issue is with using both print() and grass.info() in 
one script. Based on what I read in the guidelines, I am not clear 
whether using both is against the guidelines as such, but technically it 
seems it can cause problems as you explained (and I experienced).

>  In my script (r.vif), both approaches have an issue with how output 
> is displayed. Using grass.info <http://grass.info>() results in 
> columns not being printed with fixed width in the command output, 
> while they are in the console. On the other hand, when using print() 
> empty lines are not printed. I personally am not too much bothered by 
> both, so if you think I should use grass.info <http://grass.info>() I 
> am fine with that.
>
> First, always use the above guidelines to decide if print() or one of 
> the g.message wrappers is the right solution. Second, look at the 
> behavior in the command line (that's the canonical one). The GUI might 
> get things wrong (and that might be bug).

OK, that is good to know
>
> Please, let me know what you think about it now,
> Vaclav

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