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From: Terry Jan Reedy <tjreedy@udel.edu>
Subject: Re: Interactive interpreter hooks
Date: Mon, 03 Jun 2013 09:03:31 -0400
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On 6/3/2013 3:55 AM, Steven D'Aprano wrote:
> 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([])".

You have not said what you are actually trying to do, but you could 
definitely modify Idle to do something with user input before it sends 
it to the user process.