Run multiple exe at once in Python and read output separate

Question

I need to run multiple instances of iperf.exe tool at once (in parallel) in Python. I am using pyqt4 to create an app, which will run multiple instances of iperf.exe by a single click and need to read back the output of each instance separately. Also need to wait until all iperf instance execution completes.

I am trying to understand:

1. What would be the best approach to handle this? subprocess/qprocess/threading/multiprocessing etc.
2. How to use that approach for the above explained scenario?