How do I unindent blocks of code in Python?

It is Ctrl + [ in IDLE. You can change it to your favorite Shift + Tab in Options -> Configure IDLE - Keys. You need to restart the shell after that.

You can unindent using following keys:

In Python IDLE/Spyder: Ctrl + [
In Eclipse: Shift + Tab
In Visual Studio: Shift+ Tab
In PyCharm: Shift + Tab
In Jupyter Notebook: Shift + Tab