why should i use a executable file in python code example

Example 1: python to exe

pip install pyinstaller

cd FullPathOfFile in cmd console
pyinstaller --onefile pythonScriptName.py
# a .exe file is created in the FullPathOfFile\dist

Example 2: how to run a .exe through python

import os
os.startfile("C:\Documents and Settings\flow_model\flow.exe")