As far as I know, Geany by default uses Python 3 to run the Python codes. So in order to run Python 2 codes, do the following.
Step 1: Go to Build -> Set build commands in the menu bar (screenshot attached below).
Build -> Set Build Commands
Step 2: You would get a "Set Build Commands" window like this:
Set Build Commands window
You can clearly see the "Compile" and "Execute" build commands as
python3 -m py_compile "%f" and
python3 "%f" respectively.
Step 3: In both of these commands, change
python and you are good to go. Doing this directs Geany to call
python instead of
New Build Commands
And make sure before doing all these, save the code with a