Adding temporary output of processing algorithm to the map canvas using PyQGIS

Question

Let's say I run a simple algorithm like this

import processing
# https://docs.qgis.org/3.16/en/docs/user_manual/processing_algs/qgis/vectoranalysis.html?highlight=count%20points%20polygon#id3
processing.run("qgis:countpointsinpolygon", { 
 'POLYGONS' : 'polygons', 
 'POINTS': 'points',
 'OUTPUT': 'TEMPORARY_OUTPUT'
 })

How do I materialize/visualize/add the temporary layer in the Layers Panel?

• Taras: Check this tutorial for details: PyQGIS 101: Running Processing tools
• Taras: Also related: gis.stackexchange.com/questions/76594/…

Answer 1

Another option is runAndLoadResults().

As was mentioned in the QGIS Documentation:

Unlike when an algorithm is executed from the toolbox, outputs are not added to the map canvas if you execute that same algorithm from the Python console using run(), but runAndLoadResults() will do that.

processing.runAndLoadResults("qgis:countpointsinpolygon", { 
 'POLYGONS' : 'polygons', 
 'POINTS': 'points',
 'OUTPUT': 'TEMPORARY_OUTPUT'
 })

(But I like @MrXsquared option better, since you get the layer as a variable you can then use in the next processing steps).

• Sickboy: your version gives you the layer as a variable, too: proc = processing.runAndLoadResults("qgis:refactorfields",<<<something>>>) outputlayer = proc['OUTPUT']

Answer 2

Can't tell if that is the "best" way, but its one straight forward:

import processing
# https://docs.qgis.org/3.16/en/docs/user_manual/processing_algs/qgis/vectoranalysis.html?highlight=count%20points%20polygon#id3
proc = processing.run("qgis:countpointsinpolygon", { 
 'POLYGONS' : 'polygons', 
 'POINTS': 'points',
 'OUTPUT': 'TEMPORARY_OUTPUT'
 })
outputlayer = proc['OUTPUT']
QgsProject.instance().addMapLayer(outputlayer)