Another option is to use the "Random selection" tool for selecting N random features.

import processing

layer = iface.activeLayer()

processing.run("qgis:randomselection", {
                    'INPUT' : layer,
                    'METHOD' : 0,
                    'NUMBER' : 5 -- specify a number here
                    })

To get more information about this algorithm, please run the following command processing.algorithmHelp("qgis:randomselection") in the Python Console (Ctrl+Alt+P).

References:

• PyQGIS Developer Cookbook » 21. Cheat sheet for PyQGIS

Another option is to use the "Random selection" tool for selecting N random features.

import processing
from qgis.utils import iface

layer = iface.activeLayer()

processing.run("qgis:randomselection", {
                    'INPUT' : layer,
                    'METHOD' : 0,
                    'NUMBER' : 5 -- specify a number here
                    })

To get more information about this algorithm, please run the following command processing.algorithmHelp("qgis:randomselection") in the Python Console (Ctrl+Alt+P).

References:

• PyQGIS Developer Cookbook » 21. Cheat sheet for PyQGIS