[GRASS-dev] [GRASS GIS] #2873: Simplify usage of GRASS in Python from outside

[GRASS GIS]

#2873: Simplify usage of GRASS in Python from outside
-------------------------+-------------------------------------------------
  Reporter:  wenzeslaus  |      Owner:  grass-dev@…
      Type:              |     Status:  new
  enhancement            |
  Priority:  major       |  Milestone:  7.1.0
 Component:  Python      |    Version:  svn-trunk
Resolution:              |   Keywords:  startup, installation, scripts,
                         |  interpreter, windows installer, pygrass,
       CPU:              |  temporal, bootstrap, boilerplate
  Unspecified            |   Platform:  All
-------------------------+-------------------------------------------------

Comment (by hellik):

 Replying to [ticket:2873 wenzeslaus]:
 > To use GRASS GIS functionality in Python from outside of a GRASS
 session, i.e. without starting GRASS GIS explicitly and running a script
 (or an actual module) in the session, one needs to include approximately
 50 lines as described in the
 [https://grass.osgeo.org/grass70/manuals/libpython/script.html#module-
 script.setup grass.script.setup] manual (or in the lengthy related
 [https://grasswiki.osgeo.org/wiki/Working_with_GRASS_without_starting_it_explicitly
 wiki page]).
 >
 > Ideally, one would just do import and then one or two lines of
 initialization, for example:
 >
 > {{{
 > #!python
 > import grass.script as gscript
 > rcfile = gscript.init_data("~/grassdata", "nc_spm", "user1")
 > do_what_ever_with_grass()
 > os.remove(rcfile)
 > }}}
 >
 > == Suggestion ==
 >
 > The attached code is a prototype implementation of the Python part which
 would allow something like this. The code can only work if the following
 variables are set:
 >
 > {{{
 > #!bash
 > export GRASS_EXECUTABLE="/path/to/grass"
 > export LD_LIBRARY_PATH=$($GRASS_EXECUTABLE --config path)/lib
 > export PYTHONPATH=$($GRASS_EXECUTABLE --config path)/etc/python
 > }}}
 >
 > The `GRASS_EXECUTABLE` does not have to be set if `grass` is on the path
 or, in theory, if it is in on some standard path (e.g. `C:\Program Files
 (x86)\GRASS GIS 7.0.0\grass70.bat` on MS Windows). However, dynamic
 library path must always be set ahead (as described in #2424) for ctypes
 to work (both PyGRASS and temporal depends on ctypes). The path to Python
 packages must be set ahead as well if you want to use the initialization
 functions from the package.
 >
 > == Making it simple ==
 >
 > The three lines above might be good enough on Linux where you just dump
 it to command line or `.bashrc` but for MS Windows users it is too
 complicated. The QGIS project also considers this too much work
 ([https://github.com/qgis/qgis3.0_api/issues/9 PyQGIS bootstrap is
 complicated]).
 >
 > GRASS Python packages could go to the system packages directory, so that
 we avoid the need for setting `PYTHONPATH`. This might work well on MS
 Windows when usage of system Python is implemented as described in #2333.

 there is no ''system Python'' in windows. users always has to install
 python manually systemwide, possibly interfering with other python
 installations installed by other software.

 >
 > On Linux, `LD_LIBRARY_PATH` can be avoided if the libraries are
 installed into the system path. On MS Windows, putting more things on
 `PATH` is standard procedure from what I have seen.
 >[...]
 >Mac OS X, `DYLD_LIBRARY_PATH` can't be used anyway
 [https://lists.osgeo.org/pipermail/grass-dev/2016-January/078531.html
 since El Capitan].
 >
 > GRASS GIS executable should be on path on all platforms in the same way
 as it is on path in Linux. This is maybe not standard on MS Windows but at
 the end this is what users want (they want GRASS to be available right
 away).

 IMHO it is not a good practice to put ''everything'' in ''%PATH%'' in
 windows. ''poisoning'' %PATH% should be avoided IMHO.

--
Ticket URL: <https://trac.osgeo.org/grass/ticket/2873#comment:1>
GRASS GIS <https://grass.osgeo.org>