[Tutor] command history in a console

[W W]

On Wed, Sep 17, 2008 at 9:14 PM, Hans Dushanthakumar <
hansd at g2microsystems.com> wrote:

> G'day everyone.
>
> I'm experimenting with a custom console application, and trying to add
> command history functionality to it. It seems to basically work ok except
> for the fact that when I press the Up arrow key to run previous commands,
> the right commands are not displayed. It displays a wierd "^[[A" for each Up
> arrow key that I press. Inspite of this, when I hit enter, it DOES seem to
> run the right command.
>
> Heres a bit of code (stripped down to the bare essentials to demonstrate
> just this problem) that shows this behaviour:
>
> ------X Code starts here
>
> import readline
> import select
> import sys
> import os
>
> historyPath = ".pyhistory.test"
>
> if os.path.exists(historyPath):
>   readline.read_history_file(historyPath)
>
> inputs = [sys.stdin]   #More on this later.
>
> while 1:
>   in_ready, out_ready, ex_ready = select.select(inputs, [], [], 10)   #More
> on this later.
>   x= raw_input()
>   print "You entered: ", x
>
> ----X End of code
>
> Heres what an example run of the program looks like, with my comments:
>
> hansd at zilla:~/tools$ python test_history1.py
> ls <--------------------------------------Me: I entered "ls" here. So, this
> is the 1st command.
> ls
> You entered:  ls
> 1 <---------------------------------------Me: 2nd command "1"
> 1
> You entered:  1
> 2 <---------------------------------------Me: 3rd command "2"
> 2
> You entered:  2
> ^[[A^[[A <--------------------------Me: This is the strange characters. I
> pressed the Up key twice here.
> 1
> You entered:  1 <----------------Me: So it looks like it received the right
> command from history :"1".
>
>
> So, my question is, why does it not display the right command from history
> instead of those "^[[A" characters?
>
> It works fine if I comment out the line "in_ready, out_ready, ex_ready =
> select.select(inputs, [], [], 10)". But there is a reason why I need this to
> be there..I'm expecting input from more sources than just the keyboard.


As far as I know... ^[[A is a control character; in this case it refers to
the up-arrow keypress. I'm not sure what the select module docs mention, but
I'd bet your answer is there.

HTH,
Wayne
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