Calling QGIS from MacOS python

Question

I would like to import qgis.core and utils from my own copy of python. I do have PYQT4 installed there.

I'd be happy to add to my PYTHONPATH or sys.path.append in my code, where do the qgis modules live (on a Mac)?

Answer 1

if you use the Kyng Chaos version:

1) First solution with the PYTHONPATH variable:

Add qgis to the PYTHONPATH (terminal)

$ export PYTHONPATH=/Applications/Qgis.app/Contents/Resources/python

You can add this line to your .bash_profile

Then in Python

# Import qgis
from qgis.core import * 
QgsApplication.setPrefixPath("/Applications/QGIS.app/Contents/MacOS", True)
# init the application
QgsApplication.initQgis()

Then you can use PyQGIS

layer = QgsVectorLayer('/Users/Shared/test.shp', 'test', 'ogr')
layer.isValid()
True

2) second solution, all in Python (from Custom Initialization for running standalone PyQGIS processing.):

import os
import sys
sys.path.append('/Applications/QGis.app/Contents/Resources/python/')
sys.path.append('/Applications/QGis.app/Contents/Resources/python/plugins') # if you want to use the processing module, for example
from qgis.core import *
app = QgsApplication([],True)
QgsApplication.setPrefixPath("/Applications/QGIS.app/Contents/Plugins", True)
QgsApplication.initQgis()
import processing
....

If you use the Homebrew version , the PATHs are different (look at Homebrew-osgeo4mac)

Answer 2

Depends on how you installed QGIS. I downloaded it from qgis.org and this is where its Python packages are:

$ pwd
/Applications/QGIS.app/Contents/Resources/python
$ python -c "import qgis; print qgis.__author__"
Martin Dobias

If that's not the same for you, use the find utility to look for core.so.

Answer 3

Extending @gene's answer:

When using the osgeo4mac homebrew formula qgis2, there are two options for QGIS python standalone development:

Option 1

Appending paths inside python:

import os
import sys
sys.path.append('/usr/local/lib/python2.7/site-packages')
sys.path.append('/usr/local/lib/qt-4/python2.7/site-packages')
from qgis.core import *
app = QgsApplication([],True)
QgsApplication.setPrefixPath("/Applications/QGIS.app/Contents/Plugins", True)
sys.path.append('/usr/local/Cellar/qgis2/2.18.4/QGIS.app/Contents/Resources/python/plugins')
QgsApplication.initQgis()
import processing

It is important that both usr/local/... calls are called before from qgis.core import * and that .../python/plugin is called before import processing.

Option 2

You can extend the PYTHONPATH variable before calling python inside your terminal:

export PYTHONPATH=/usr/local/Cellar//qgis2/2.18.4/QGIS.app/Contents/Resources/python/:/usr/local/lib/qt-4/python2.7/site-packages:/usr/local/lib/python2.7/site-packages:$PYTHONPATH")

This approach is also noted in brew info qgis2:

For standalone Python development, set the following environment variable: export PYTHONPATH=/usr/local/lib/qt-4/python2.7/site-packages:/usr/local/lib/python2.7/site-packages:$PYTHONPATH

I do also recommend setting the QGIS env variable QGIS_DEBUG=1 to suppress debug output messages during your processing calls:

export QGIS_DEBUG = -1

Currently, I also export the following two lines before calling python:

export DYLD_LIBRARY_PATH=/usr/local/Cellar/qgis2/2.18.4/QGIS.app/Contents/MacOS/lib/:/Applications/QGIS.app/Contents/Frameworks/
export QGIS_PREFIX_PATH=/usr/local/Cellar/qgis2/2.18.4/QGIS.app/Contents/MacOS/

However, I'm not sure if this is really necessary. Might delete/update it once I did more testing or received some feedback.