PyQGIS – How to Add Variable to Print Layout using QGIS

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I have a QGIS workspace (3.26) containing several vector and raster datasets. I plan to produce multiple print layouts from this workspace to display information such as the site location, predicted flood extents, LiDAR levels, etc. on separate maps.

I am in the process of writing a short python script and UI to help users specify variables at the project level such as a project name/number and a client name. These values will then inform all print layouts. I'm using code similar to the snippet below to achieve this:

QgsExpressionContextUtils.setProjectVariable(QgsProject.instance(), 'clientName','Dave')

These project level variables work for values that do not change between print layouts such as the client name, but I'm looking to add some more variables at the print layout level – e.g. plot name. Is there a print layout equivalent to the code above to set a variable to a map rather than the project?

Best Answer

There is the function QgsExpressionContextUtils.setLayoutVariable which takes a QgsLayout as a first parameter, maybe that would be what you can use?

Documentation is at https://qgis.org/pyqgis/3.26/core/QgsExpressionContextUtils.html#qgis.core.QgsExpressionContextUtils.setLayoutVariable

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2) You can also use R from Python with the rpy2 module and Python from R with the RPython package

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PyQGIS Print Layout – Print Layout Legend and setLegendFilterByMapEnabled()

You need to link the legend item to a map item in your layout which is an instance of the QgsLayoutItemMap class. So if you have done something like:

map = QgsLayoutItemMap(layout)
layout.addItem(map)

link it with the legend before enabling the filtering:

legend.setLinkedMap(map) # pass a QgsLayoutItemMap object
legend.setLegendFilterByMapEnabled(True)
legend.refresh()

Alternatively, to collect checked layers from the project layer tree view and add those to your layout legend, you could do something like this:

lyrs_to_add = [l for l in QgsProject().instance().layerTreeRoot().children() if l.isVisible()]
legend = QgsLayoutItemLegend(layout)
legend.setTitle('Legend')
legend.setAutoUpdateModel(False)
group = legend.model().rootGroup()
group.clear()
for l in lyrs_to_add:
    if l.nodeType() == 0:
        subgroup = group.addGroup(l.name())
        checked = l.checkedLayers()
        for c in checked:
            subgroup.addLayer(c)
    elif l.nodeType() == 1:
        group.addLayer(l.layer())
layout.addItem(legend)
legend.adjustBoxSize()
legend.refresh()

This will maintain groups etc. but unfortunately it won't filter unchecked nodes for categorized or graduated layers (I still can't work out how to do that).

Best Answer

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PyQGIS Print Layout – Print Layout Legend and setLegendFilterByMapEnabled()

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