Starting QGIS Desktop with Python script

Question

I looked at the QGIS official documentation (e.g., Using PyQGIS in custom applications) and a few questions here (e.g. Running QGIS through Python), but I was unable to find an example of a Python script that starts a regular QGIS app.

In other words, I look for the 'official'/recommended way to replicate the same results of running QGIS.exe (splash screen, main window visualization, etc.) using a qgis.py instead (i.e., without calling a QGIS executable using subprocess):

import logging
from qgis import core

logger = logging.getLogger(__name__)


def main():
    qgis_version = core.Qgis.version()
    logger.info('Running QGIS v.%s ...' % qgis_version)

    qg = core.QgsApplication([], True)
    qg.initQgis()

    # some code here that runs the QGIS splashscreen?

    # some code here that shows the QGIS main window?
    
    qg.exec_()
    qg.exitQgis()

    logger.info('Running QGIS v.%s ... DONE' % qgis_version)

(I am aware that it is possible to execute a startup.py, but this question is about writing a Python script that starts QGIS up.)

Answer 1

You can use the pattern in the script:

from qgis import core
import subprocess

def main():
    qg = core.QgsApplication([], True)
    qg.initQgis()

    print("Starting QGIS")
    
    qgis_exe = r"C:\OSGeo4W64\bin\qgis-bin.exe"
    process = subprocess.Popen(qgis_exe, shell=True, stdout=subprocess.PIPE)
    process.wait()
    
    qg.exitQgis()

    print("QGIS is closed now")

main()