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I am trying to generate maps in pdf files by using a pre-defined .qgz layout. I am already able to load layers and adjust color scale, etc. Since the legend is synchronized with the map layers, all the layers I have loaded are listed in the legend.

Using PrintComposer in QGIS I can turn off synchronization and remove the unwanted items in legend. Is there a way to do it automatically in Python? I tried to use QgsLegendModel, but it also removes the layers from map canvas.

unwanted items in legend.

projectInstance= QgsProject.instance()
projectLayoutManager = projectInstance.layoutManager()

for comp in projectLayoutManager.printLayouts():
    for item in comp.items():
        if(isinstance(item, QgsLayoutItemLegend)):                
            model = item.model()
            while model.rowCount()>1:
                 model.removeRow(0)

            break
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2

This is code adapted for QGIS 3 from this answer. It adds all layers except one specified. You could swap this out for a list, or conversely, use the layers you want to keep in rather than those you want to leave out.

l = QgsProject.instance().layoutManager()

for layout in l.printLayouts():    
    legend = QgsLayoutItemLegend(layout)
    root = QgsLayerTree()
    for lyr in iface.mapCanvas().layers():
        if lyr.name() != 'Unwanted layer':  
            root.addLayer(lyr)
        legend.model().setRootGroup(root)
        layout.addItem(legend)

In place of if lyr.name() != 'Unwanted layer': you could use

if lyr.name() not in [list, of, unwanted, layer, names]: or

if lyr.name() in [list, of, wanted, layer, names]:

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  • iface.mapCanvas().layers() returns an empty list when run within the script. However when I paste it in Python console it returns correct collection of layers. I guess there is an asynchronous update for which I should wait for? – Marcin Kawka Dec 18 '18 at 13:54
  • Are you using a standalone script or one in the Editor in the Python console? – Matt Needle Dec 19 '18 at 12:43
  • I am using Python Editor (within QGIS 3.4) – Marcin Kawka Dec 19 '18 at 12:50
  • That is strange. Mine works as desired. It won't include layers which are unchecked in the layers panel, however. – Matt Needle Dec 19 '18 at 12:53
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Matt Needle, your solution started to work after I've forced qt to process the bufferd events, before iterating through layers. Thank you for your hint. 


from PyQt5 import QtWidgets
inst = QtWidgets.QApplication.instance()
qapp = QtWidgets.qApp
qapp.processEvents()

l = QgsProject.instance().layoutManager()

for layout in l.printLayouts():    
    legend = QgsLayoutItemLegend(layout)
    root = QgsLayerTree()
    for lyr in iface.mapCanvas().layers():
        if lyr.name() != 'Unwanted layer':  
            root.addLayer(lyr)
        legend.model().setRootGroup(root)
        layout.addItem(legend)
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