How to source setup.bash before running a launch file with RosLaunchParent in python?

edit

I'm trying to launch my launch file with the python API, something like this

mylaunch = roslaunch.parent.ROSLaunchParent(uuid, roslaunch_file, force_log=True)
mylaunch.start()

But the issue is, I have to source the setup.bash file before I start my launch file. Is there an API to do it? If not how do I achieve it? Because without sourcing I dont see the updated parameters that my launch file reads from.

Thanks in advance!