Calling a plugin (QuickOSM) from a Python standalone application?

Question

I am trying to call the QuickOSM QGIS plugin from a standalone Python application and I ́m not quite sure how to or if this is even possible.

My QGIS version is 3.10 (using OSGeo4W64) with the QuickOSM plugin installed. Running on Windows.

I tried to achieve this by using QGIS Processing, but I failed.

import sys
import os
import qgis
from qgis.gui import *
from qgis.core import *
from PyQt5.QtCore import *
QgsApplication.setPrefixPath("C:\\OSGeo4W64\\apps\\qgis\\", True)
qgs = QgsApplication([], False)
qgs.initQgis()
qg_project = QgsProject.instance()
from qgis.analysis import QgsNativeAlgorithms
import processing
from processing.core.Processing import Processing
Processing.initialize()
qgs.processingRegistry().addProvider(QgsNativeAlgorithms())
# The extent is calculated somewhere else
alg_params = {'EXTENT': my_extent,
 'KEY': '',
 'SERVER': 'http://www.overpass-api.de/api/interpreter',
 'TIMEOUT': 25,
 'VALUE': ''
 }
feedback = QgsProcessingFeedback()
outputs['BuildQueryInsideAnExtent'] = processing.run('quickosm:buildqueryextent', alg_params, feedback)
qgs.exitQgis()

This fails, stating algorithm quickosm:buildqueryextent not found. When I try to call QGIS native, GDAL or GRASS algorithms, processing works.

I haven't found a solution to this. Maybe I can tell the script somehow where to find the plugin scripts? Is such a call even possible? Or do I have to do it another way all together?

Answer 1

Your error is around here:

qgs.processingRegistry().addProvider(QgsNativeAlgorithms())

Your are adding only QGIS native algorithms in your Processing. QuickOSM is a plugin and is not in the QgsNativeAlgorithms.

The way to do that might be differente since version 3.8. You should be able to do the initProcessing() function somehow, but I haven't checked.

from qgis.utils import plugins
plugins['QuickOSM'].initProcessing()

But I don't think it will work. (but it would be the best and cleaned way).

As a workaround, you can still do

from QuickOSM.quick_osm_processing.provider import Provider
QgsApplication.processingRegistry().addProvider(Provider())

Note that you are in standalone executable. You need first to enable QuickOSM in your application. This is possible.

• ThomasG77: I've an uncomplete script to try to solve the issue at gist.github.com/ThomasG77/71def7a758bfa75425d5bc87dde68906 If you have any clue, do not hesitate
• etrimaille: I will have a look to your script @ThomasG77. I think the plugin is not known by QGIS and needs to be loaded by QGIS. I'm not sure.
• ThomasG77: In standalone context, from qgis.utils import plugins followed by a print(plugins) returns empty dict (because no iface, so not automatic plugin loading I think)...
• etrimaille: Either wait for QGIS 3.14, or have a look to this pull request to check how it is done github.com/qgis/QGIS/pull/34617
• etrimaille: You can have a look to this code. It's working well to load a custom plugin processing provider : github.com/3liz/qgis-lizsync-plugin/blob/master/processing/…

Answer 2

I was going through the quick_osm code and thought doing this might work, which actually did!

from QuickOSM.quick_osm import QuickOSMPlugin
QuickOSMPlugin.initProcessing(QuickOSMPlugin)

You can verify the QuickOSM processing algorithms by:

for alg in QgsApplication.processingRegistry().algorithms():
 print(alg.id(), "->", alg.displayName())

-->

.
.
.
qgis:vectorlayerhistogram -> Vector layer histogram
qgis:vectorlayerscatterplot -> Vector layer scatterplot
qgis:voronoipolygons -> Voronoi polygons
quickosm:buildqueryaroundarea -> Build query around an area
quickosm:buildquerybyattributeonly -> Build query by attribute only
quickosm:buildqueryextent -> Build query inside an extent
quickosm:buildqueryinsidearea -> Build query inside an area
quickosm:buildrawquery -> Build raw query
quickosm:openosmfile -> Open sublayers from an OSM file

or,

processing.algorithmHelp("quickosm:buildqueryextent")

Answer 3

The answer here did what I needed: Access the plugin (QNEAT3 in my case) and run its algos in standalone. May not work with every plugin, but is not the big hack I was worried about.