PYQGIS 3: Save custom layout in .qgs project

Question

I iteratively create .qgs projects, load different layers in them, create a layout and export the maps. The .qgs projects are created but when I open them, my custom layout is not there! Therefore it was not saved within the project. What did I miss?

Here is my piece of code:

processing_name = ["qgs_t1", "qgs_t2", "qgs_t3"]
anriss_list = ["C:\\MyData\\A300.shp", "C:\\MyData\\B300.shp", "C:\\MyData\\C300.shp"]
anriss_name_list = ["A300","B300","C300"]

for i in range(len(3)):
    # create project
    qgis_project_name = "C:\\ResultFolder\\" + processing_name[i] + ".qgs"

    project = QgsProject.instance()
    project.setCrs(QgsCoordinateReferenceSystem(21781))

    # add vector layer
    iface.mainWindow().blockSignals(True)
    shplayer = iface.addVectorLayer(anriss_list[i], anriss_name_list[i], "ogr")
    if not shplayer.isValid():
       print("Anriss .shp failed to load!")
    shplayer.setCrs(QgsCoordinateReferenceSystem(21781))

    project.addMapLayer(shplayer)

    #-- Create custom caneva
    manager = project.layoutManager()
    layout_name = 'my_custom_layout'
    layout_list = manager.printLayouts()

    layout = QgsPrintLayout(project)
    layout.setName(layout_name)
    layout.initializeDefaults()
    manager.addLayout(layout)

    #--- create map item

    map1 = QgsLayoutItemMap(layout) # create Layout item
    map1.setRect(QRectF(10, 10, 210, 90)) # set the map item rectangle
    map1.setPos(10,10) # map item upper left corner position
    map1.setFrameEnabled(True) # to have a map black border

    ms = QgsMapSettings()
    ms.setLayers([shplayer]) # set layer to be mapped
    map1_extent = QgsRectangle(shplayer.extent())
    map1_extent.scale(1.0)
    ms.setExtent(map1_extent)
    map1.setExtent(map1_extent)

    layout.addLayoutItem(map1)
    map1.attemptMove(QgsLayoutPoint(10,10))
    map1.attemptResize(QgsLayoutSize(210,90))


    # export map in .pdf
    exporter = QgsLayoutExporter(layout)
    exporter.exportToPdf("C:\\mapstest.pdf", QgsLayoutExporter.PdfExportSettings())


    project.write(qgis_project_name[i])
    project.clear()

Answer 1

Oh that was a missing line "project.write()" before exporting the .pdf! Problem solved