Setting new size for printLayout using PyQGIS

Question

I am trying to create an A0 layout from PyQGIS. I tried the following code but it doesn't work.

from qgis.core import *

manager = QgsProject.instance().layoutManager() 
layouts_list = manager.printLayouts()
for l in layouts_list:
    l.clear()

layout = QgsPrintLayout(QgsProject.instance())  
layout.setName("TEST")
layout.initializeDefaults()
page = QgsLayoutItemPage(layout)
pageSizes = QgsPageSizeRegistry()
pageSize = pageSizes.find("A0")[0]
orientation = QgsLayoutItemPage.Landscape
valid = page.setPageSize(pageSize.displayName, orientation)
print(valid, page.pageSize().width(), page.pageSize().height(), page.orientation())

manager.addLayout(layout)

When I execute this code the layout is created and I get the following message in the console:

True 1189.0 841.0 1. True means that the setPageSize was a success and the sizes are correct.

But when I open the layout in the interface I always get an A4 page.

Am I doing something wrong?

Answer 1

Try using the following which uses the pageCollection() method to manage the page settings:

layout = QgsPrintLayout(QgsProject.instance())  
layout.setName("TEST")
layout.initializeDefaults()
pc = layout.pageCollection()
pc.pages()[0].setPageSize('A0', QgsLayoutItemPage.Orientation.Landscape)
manager.addLayout(layout)

Answer 2

typo : The orientation belongs directly to QgsLayoutItemPage

from qgis.core import *
manager = QgsProject.instance().layoutManager() 
layout = QgsPrintLayout(QgsProject.instance())  
layout.setName("TEST")
layout.initializeDefaults()
pc = layout.pageCollection()
pc.pages()[0].setPageSize('A0', QgsLayoutItemPage.Landscape)
manager.addLayout(layout)

This code works.