[GIS] How to use two different Python versions (3.4 and 2.7) for QGIS scripting

pyqgispython 3qgis

I´m intending to learn scripting with python in QGIS, but I have a couple of questions.

I'm using Python 3.4 for learning which is installed in my laptop, but QGIS is using Python2.7

How could I work with both together?
Creating an enter in the PYTHONPATH like C:……….python27 (wherever it is into QGIS directory) and adding a shebang #!…..python27 at the begining of my scripts?

Is there another way to work with both versions ?

I´m using PyQT and the same question again. One designer in python3.4 installed and another one into the QGIS directory.

How do you work?

Best Answer

I ran across this problem and came to a solution. I added a question/answer post to add some insight to this problem: Using PyQGIS, ArcPy, NumPy, SciPy Together in Windows Command Prompt

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[GIS] How to Setup Python to recognize QGIS

It looks like you have a similar problem to one I had. Though the specifics of the paths are different I believe that a similar solution can work. See my solution in this post.

What is happening is that it is not just the PYTHONPATH which is read but also the PATH variable. On load QGIS appends the paths of the osgeo binaries to the path, which means they get read last. That means the ArcGIS location is found first and Windows looks no further.

What you don't want to do is muck up your ArcGIS install by playing with the main PATH variable (where there will be a reference to the Arc Python directory). However, if you tell QGIS to reverse the sys.path variable as the first thing it does, it will read the osgeo paths first and ignore the Arc Python instalation. This change is only apparent within the specific Python session (i.e. it has no effect on the actual PATH or PYTHONPATH variables stored on your computer and neither is it permanent, so will be safe as far as ArcGIS is concerned and less dangerous than editting your PATH variable as this could end up breaking Arc with the same problem but the other way around).

Depending on your install, you might want to change my solution to something like (based on what I read in your question):

import sys
sys.path.extend([r"C:\Quantum_GIS_Lisboa\apps\qgis\python",r"C:\Quantum_GIS_Lisboa\apps\qgis\bin"])
sys.path.reverse()

If you have used osgeo4w to install QGIS this will be unnecessary, but you could do it anyway as a belt-and-braces approach - it won't hurt). I suspect you will also need to add the lines at the start of the set_qgis_01.py file (I did mine in the GDALTOOLS.py file because that's where my conflict manifested itself).

[GIS] Setting up Python 2.7 to work in both QGIS and ArcGIS Desktop

While you can do it with the standalone installed copy of QGIS I would highly recommend installing QGIS and QGIS-dev using the OSGeo4W installer. OSGeo is easier to update and lets you get the latest stuff.

That will install Python into C:\OSGeo4W\app\Python27 and let you run Python from the OSGeo4W shell. python.exe lives in C:\OSGeo4W\bin.

I have some examples of QGIS stuff at https://github.com/NathanW2/pyqgis-playground

Use the following batch file as a bootstrap to your python file:

@ECHO OFF
set OSGEO4W_ROOT=C:\OSGeo4W
set PATH=%OSGEO4W_ROOT%\bin;%OSGEO4W_ROOT%\apps\qgis-dev\bin;%PATH%
SET PYTHONHOME=%OSGEO4W_ROOT%\apps\Python27
set PYTHONPATH=%OSGEO4W_ROOT%\apps\qgis-dev\python
set QGIS_PREFIX_PATH=%OSGEO4W_ROOT%\apps\qgis-dev\

Best Answer

Related Solutions

[GIS] How to Setup Python to recognize QGIS

[GIS] Setting up Python 2.7 to work in both QGIS and ArcGIS Desktop

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