What is the new expression of setSelectedFeatures in PyQGIS 3.0 ? I wrote the following code:

def verCode(layername):
  layer = QgsProject.instance().mapLayersByName(layername)[0]    
  selection= layer.getFeatures(QgsFeatureRequest().setFilterExpression('"CODE_MERC" is NULL'))
  layer.setSelectedFeatures([s.id() for s in selection])

1 Answer 1


According to the pyqgis api documentation there is a method

layer.selectByIds([s.id() for s in selection])

And for some performance improvements and good practice, don't request any attributes or geometry, if you only need the feature id

request = QgsFeatureRequest(QgsExpression('"CODE_MERC" is NULL')).setFlags(QgsFeatureRequest.NoGeometry).setSubsetOfAttributes([])
selection = layer.getFeatures(request)
  • Many thanks Matthias. It is very helpful. However, for the QgsFeatureRequest expression, I receive an error : TypeError: QgsFeatureRequest(): arguments did not match any overloaded call. Perhaps, I wrote it in the wrong way in my code. Could you please write it explicitly in my code?
    – ennine
    Commented Sep 22, 2018 at 9:14
  • It probably was an error on my side. Does it work if you do QgsFeatureRequest(QgsExpression('"CODE_MERC" IS NULL')).setFlags(... Commented Sep 22, 2018 at 9:35
  • No error but nothing happen. I am sorry, but I did not know where to place the obtained "request" in the code. Note that "request" expression is not attached to any layer.
    – ennine
    Commented Sep 22, 2018 at 10:29
  • I updated the sample, is it better now? Btw, nothing should change, it's just "good practice" to request only what is actually needed. Commented Sep 24, 2018 at 6:09

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