Python used to run smoothly on my macbook, but since I opened the debugger yesterday, the IDLE window cannot be opened anymore. It shows an error message "IDLE's subprocess didn't make connection". 

I tried to uninstall everything and download it again from the website, but the problem is unsolved. I am using the latest OS X Mountain Lion, and installed Python 3.3.2 and the latest Tcl/Tk. Please advice me how to fix the problem.

To help see what the problem is open a Terminal shell window and type:
cd $HOME
ls -l .idlerc/*
cat .idlerc/*

Then try typing:
/usr/local/bin/idle3.3

If that fails, try:
/usr/local/bin/idle3.3 -n

For all of the above, please update this issue with a copy and paste of the resulting outputs.

Thanks Ned,

I have solved the issue by deleting all my previous py files on my computer. But I couldn't figure out what really triggered this error, as those files did not create any problems before.

If deleting .py files solved the problem, you probably had created a .py file with the same name as a Python standard library module.  If that file is in your Documents folder (if you are using /Applications/Python3.3/IDLE.app) or your current working directory (if you use /usr/local/bin/idle3.3), that directory is inserted first on Python's search path for modules and the files there will be found before the normal standard library version.  For example, if you create a dummy text file named socket.py in Documents and then double-click on IDLE.app, you should see the same message that the subprocess didn't make a connection because the dummy socket.py shadows the standard library socket module.  In any case, I'm glad that the problem is resolved for you.