PyQGIS: Get Info From Layers in the QGIS Interface

Objectives:

• Get information from layers that have already been added to the QGIS interface

Open the QGIS Python Console

From the menu, select Plugins -> Python Console, or Ctrl + Alt + P (Windows)

You can type directly into the console, or select the pad and paper icon to write code in the editor. I prefer to write code in the editor because it allows me to save my work and run a compilation of commands.

Get layers by name

The simplest way to get layer information from layers in the QGIS interface is to use the layer name. We can use the mapLayersByName() function to retrieve an object containing all the layers with a given layer name. The code below retrieves all layers with the name ‘dem’.

layers = QgsProject.instance().mapLayersByName('dem')

If more than one layer had the name ‘dem’ the layers object will contain the information for multiple layers. We can determine the number of layers by finding the length of layers.

print(len(layers))

Output:

1

In this case there is just one layer.

Getting layer information

Information from the layer can now be retrieved with layers[0] to get the first layer. For example we could get the layer name with the code below.

print(layers[0].name())

Output:

dem

This is a raster layer, so we could also get information like width, height, and band count. For example.

print(layers[0].width(), layers[0].height(), layers[0].bandCount())

Output:

45 45 1

If there were multiple layers with the name ‘dem’, we could loop through each layer in the layers object, printing information for each one as follows.

for layer in layers:
    print(layer.bandCount(), layer.height(), layer.width())

An important attribute of the layer is its file name. We can access the file name as follows.

print(layers[0].dataProvider().dataSourceUri())

Output:

path/to/file/name

Video tutorial

See this tutorial described in a video.