1. start IDLE
“Python 2.5”→“IDLE（Python GUI）”
2. open your source file window
From python shell, select file->open...
3. show debug control
From python shell, select Debug->Debuger
4. start running
From the source file window, select Run->Run Module
5. debugging with Debug Control
Step: step into
Over: step over
Out: step out
Go: run...
breakpoint: set and clear breakpoint in the source file window with right click menu at the line you want