Summary:
Windows User, that has python installed on his/her machine, double-clicks a (.py) or (.bat) file and it launches myapp.py in the Python Idle Shell.
Alternatively, the myapp.py is able to launch itself in Python Idle Shell after getting double clicked but that is probably not feasible.
More rambly (to prevent misunderstanding):
If someone wants to run a (.py) file via Python Idle Shell, they would right-click on the file > 'Edit with IDLE' > 'Run Module (F5)'. How can I run the (.py) file via Python Idle Shell with just double-clicking a (.py) file or (.bat) file?
Additional info
OS: Windows 7 (x64)
Python: 2.7
python myapp.pybut it wouldn't use IDLE.idleand used it's-rcommand-line option to run the .py file. Here's the documentation on Idle's Command line usage.