What is the second argument in QgsProcessingUtils.mapLayerFromString()?

Question

I am new to Qgis3. I am trying to get a layer in the Python console. And I have to put to arguments in the function QgsProcessingUtils.mapLayerFromString(). The first argument is self-explanatory, the string. But I don't understand what the second argument is (the QgsProject).
Could someone clarify me what that second argument is?

Luis Perez · Answer

There are several ways to access the layers.
As @christoph tells you, it is easier and more direct to use the methods of QgsProject.
We start by instantiating pry=QgsProject.instance()
1.- To access a layer by its name you can use
pry.mapLayersByName()

It returns a list, because you can have several layers with the same name. If only one layer matches, you can access it by its index:
pry.mapLayersByName("transport")[0]

2.- From QGIS3.10 you also have the mapLayersByShortName() method
3.- If you want a list with all the layers:
pry.mapLayers()

Returns a dictionary, the layer id is the key
On the other hand, you can combine with the methods of iface (QgisInterface) and QgsMapCanvas
1.- Get the active layer**:

iface.activeLayer() returns the active layer
iface.mapCanvas().currentLayer() generates the same result

2.- A list of the layers visible on the canvas
iface.mapCanvas().layers()

What is the second argument in QgsProcessingUtils.mapLayerFromString()?

One Answer

Add your own answers!

Ask a Question