What is happening:
>>> 2 * 10
2 * 10
20
>>>
What I want to happen:
>>> 2 * 10
20
>>>
Does anyone know why the command is printed out before being executed and how to stop it from doing that? I can't find any documentation about this. I'm using Emacs 23 on Mac OS X with Python 2.7.
I don't use python, but I would guess that the python feature you are using has set the variable comint-process-echoes incorrectly. Whatever the value in your buffer is, just reverse the boolean value.
Comint is a support library in Emacs for running inferior processes in Emacs. It interacts with the prompts, and the python shell (or M-x shell) needs to be told about the echo feature.
In your shell buffer with the problem, do:
M-: (setq comint-process-echoes t) ;; or nil
