Interactive interpreter hooks in python

Question

The sys module defines two hooks that are used in the interactive interpreter:

• sys.displayhook(value) gets called with the result of evaluating the line when you press ENTER;

• sys.excepthook(type, value, traceback) gets called with the details of the exception when your line raises an exception.

Is there a way to hook into the interactive interpreter *before* it is evaluated? That is, if I type "len([])" at the prompt and hit ENTER, I want a hook that runs before len([]) is evaluated to 0, so that I get the string "len([])".

Answer 1

I dont know whether that is possible, but you could recreate the repl. This page seems to have good resources for that: http://stackoverflow.com/questions/1395913/python-drop-into-repl-read-eval-print-loop

A trace function could also work. See docs for sys.settrace. The source code for the python GOTO module is a good example of its usage.

Answer 2

You will need to write your own REPL for this. Use the code.InteractiveConsole class:
http://docs.python.org/2/library/code

I recommend source-diving to see what you need to override, but I suspect you can just wrap around the runsource() method.