How to print automatically Map themes in Label's Map Composer?

Question

This expression [%@project_path%] prints the path of the qgis project.

How the Map Theme used in the layout can also be printed automatically ?

According to QGIS documentation, a Map Theme is a snapshot of the current map legend that records.

How to reproduce the issue

The Map Theme is set according to these steps :

1. View tab > Panels > Layers

2. Click on the Manage Map Themes icon > Add Theme

3. Give the new Map Theme a name

4. Open a new Print Layout > click on Adds a new Label to the Layout > create one

Issue

Does a variable or an expression exist to automatically print the name of the Map Theme in the Print Composer?

Answer 1 (not entirely satisfactory)

1. create manually a Map Theme
2. open Python console > iface.mapCanvas().setTheme('your theme')
3. open Print Composer > add a new map to the layout > Item propriety tab > Item ID > write what you want

4. add a new Label to the Layout > item propriety > click insert an expression button > function editor tab > click '+' button > insert the code below :

   from qgis.core import * from qgis.gui import * from qgis.utils import iface

   @qgsfunction(args='auto', group='Custom') def print_theme(value1, feature, parent): return iface.mapCanvas().theme()

5. Expression tab > print_theme('_your_map_id_')

Answer 1

An atlas could do the job and even set the theme (or preset) for each image in case you have more than one:

1. Create a layer to guide the atlas and themes:
2. Control the composer by atlas.
3. In the map options, set the the layers followed by function and then:
4. Select the atlas attribute that defines the theme. (This name must be exactly the same as the defined in the theme layers).
5. Show the theme attribute in the text box.

Here the screenshots of the process. I hope it helps.