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Best practices for writing Python QGIS Expression Functions

Recently there have been some questions and discussions about python based expression functions and how parameters like usesGeometry  need to be used. So I thought I’d quickly write down how this works. There is some intelligence If the geometry or a column is passed in as a parameter you do not need to request it manually, you can even specify explicitly that you do not require the geometry or a column here. @qgsfunction(args=’auto’, group=’Custom’, usesGeometry=False, referencedColumns=[]) def Read more…

By Matthias Kuhn, ago

QGIS Expressions Engine: Performance boost

Expressions in QGIS are more and more widely used for all kinds of purposes. For example the recently introduced geometry generators allow drawing awesome effects with modified feature geometries on the fly. The last days at the QGIS developer meeting 2017, I spent some time looking into and improving the performance for expressions. This was something that was on my todo list for a while but I never got around to working on it. Short Read more…

By Matthias Kuhn, ago

QGIS2 compatibility plugin

Lately I’ve been spending time porting a bigger plugin from QGIS 2.8 to 3 while maintaining 2.8 compatibility. You can find it at https://github.com/opengisch/qgis2compat/ and https://plugins.qgis.org/plugins/qgis2compat/ One code to rule them all. My target was to have to edit the source code as little as possible to simulate a lazy or busy coder that has to upgrade his/her plugins. Lots of work has already gone into 2.14 to support PyQt 4 and 5 with the Read more…

By Marco Bernasocchi, ago

Updating PyQt signals that use lambda in QGIS with 2to3

Just for the sake of documenting things, when running qgis 2to3 on a plugin I encountered a tricky situation regarding signals. MYQGISDIR/scripts/2to3 -f signals -w my/plugin/path The original code: extra_arg = “my test argument” QObject.connect( action, SIGNAL( “triggered()”), lambda extra_arg=my_arg: show_extra_arg(extra_arg)) def do_load_project(extra_arg): print extra_arg # “my test argument” The generated code: extra_arg = “test_arg” action.triggered.connect( lambda extra_arg=my_arg: show_extra_arg(extra_arg)) def do_load_project(extra_arg): print extra_arg # False so in do_load_project we get False instead of “my test Read more…

By Marco Bernasocchi, ago

QGIS: Qt5 and Python3 migration, current state

Behind the scenes a lot has happened to get ready for Qt5 and Python3. On the same codebase that is becoming the next release QGIS 2.16. This is really a great thing since we can focus work on a single master branch and I’m very happy that we got so far with this approach already. Testing At OPENGIS.ch we have put a huge effort into getting the Travis CI test infrastructure to test our code with Qt5 Read more…

By Matthias Kuhn, ago

Prepare your plugins for QGIS 3

QGIS 3 is not yet there and there is still plenty of time to prepare and migrate. But I thought I would give some advice about things that you can keep in mind while working on your plugins to make your life easier when you will have to actually do the migration. It’s mostly about making your code prepared for Python 3 and PyQt5. Do not use star imports Don’t do from PyQt4.QtCore import * Read more…

By Matthias Kuhn, ago

Increasing the stability of processing algorithms

Processing just got a new testing framework to improve the long-term stability of this important plugin. And you can help to improve it, even if you are not a software developer! This is yet another piece in our never-stopping crusade to improve the stability and quality of the best desktop GIS on the market. Processing You probably know processing. If you don’t: processing is the number one plugin to enable after every QGIS installation. It offers a Read more…

By Matthias Kuhn, ago

QField Documentation

After getting QField up and running in Android 5, we felt it was time to start documenting how QField works, we started documenting how to install and use QField. We also added a section on how to handle your data to get them on QField. It is all pretty basic, but it dose give some hints. You can find the documentation here: https://qfield.org/docs/ As QField’s source code the docs are opensourced (on github) and we look Read more…

By Marco Bernasocchi, ago