I try to use native algorithm difference of QGIS. But it seams it doesn't work like the others :

parameters = {'INPUT': polygons['OUTPUT'], #from temporary layer created before
              'OVERLAY': layer, #read in the beginning with QgsVectorLayer
              'OUTPUT': 'memory:'}
differenced = processing.run('qgis:difference', parameters)

I get the following error :

_core.QgsProcessingException: There were errors executing the algorithm.

Both input and overlay layers have the same geometry. Any idea ?


I had similar problem and I found your question whilst searching for a solution. I see it's been five months though, so i guess you've found a solution already - if not, the script I use below works for me (i'm currently using QGIS 3.4.3).

A = QgsProject.instance().mapLayersByName('t_alpha')[0]
B = QgsProject.instance().mapLayersByName('t_beta')[0]

parameters = {'INPUT' : A, 'OVERLAY' : B, 'OUTPUT' : 'memory'}

results = processing.runAndLoadResults('qgis:difference', parameters)

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