[Python-ideas] Default value for input

[Steven D'Aprano]

On Tue, Apr 01, 2014 at 03:21:40PM +0100, Paul Moore wrote:

> Windows has much richer line editing capabilities than "plain old
> backspace" - sufficiently so that I end up very frustrated when
> working on Unix programs that don't have readline support, because
> they are *so* limited (no arrow keys? seriously?).

Sorry, I didn't intend to put down the Windows editing experience, it's 
not something I've had much experience with in Python. And you are 
right, Python on Linux without readline support is *painful*.


> Ignoring that point, though, pre-filled edit buffers are *extremely*
> uncommon on Windows, and I would imagine them being very surprising to
> a user. I'm not sure I've ever seen them on Unix either, 

Pre-filled buffers are quite common in curses applications like the 
mail-client mutt or the editor nano.

I'm hoping for something lightweight and cross-platform, which rules out 
curses.

> though, so
> maybe the target audience for this has specialised or unusual
> expectations? 

Well, yes, they would be users of console apps who expect user 
*friendly* text interfaces instead of the user-hostile ones most 
developers write *wink*


> Personally, I'm used to (and comfortable with) the
> "Enter a value [12]: " convention where this means that pressing enter
> without providing a value gives 12 (and I'd just implement that
> manually with if val='': val = '12').

That's fine for the typical "[Y]/n" one letter inputs that are extremely 
common, and I don't have a problem with that. But for longer text, the 
inability to modify the default except by retyping the entire thing is a 
pretty major failure of the user interface. Imagine if the only way to 
get a default value in your GUI or web app's edit field was to put a 
label next to it:

Leave the field blank to accept "Something" as the default.
Type a thing here: _______________________________


I wouldn't accept that in my GUI apps, and I don't think that it's 
acceptable in console apps either.


> I'm not sure how easy it would be to implement for Windows. I've never
> needed it, so I've never looked into it.
> 
> -1 on it being a builtin capability of input(). -0 on it being a
> separate builtin or stdlib function (mainly because I don't think it's
> needed often enough to be worth it). It seems to me it'd be fine as a
> package on PyPI, or maybe a recipe.

I obviously don't agree with you, but I appreciate the comments. 
Regardless of what happens in 3.5, I'll look at putting something up on 
PyPI, although chances are it will require readline support and won't be 
platform-independent. That will limit its use drastically.



-- 
Steven