[Tutor] changing list index start

[Steven D'Aprano]

On Sat, 11 Sep 2010 11:25:12 pm Rance Hall wrote:

> Thanks everyone for responding,  Because this menu structure is
> repeated many times in my code, the ideal solution would have been to
> "set index start = 1" in the beginning of the script.

That is exactly the wrong solution. That will break anything and 
everything that assumes "set index start = 0" is applying. Fortunately 
Python doesn't allow such a bad "solution".

The right solution is to get rid of all that duplicated code. Put the 
menu structure in one place, a function, and then call that function 
whenever you need it:


def display_menu(menu):
    for i,option in enumerate(menu, 1):
        print('%s. %s' % (i, option))
    choice = int(input('\nYour Choice? '))
    clearscreen(osname)
    return choice-1


Now your mainmenu function becomes:

def mainmenu():
    # the main menu, in case you can't read the function name
    todolist()  # why is this here? 
    menu = ['Clients','Jobs','Billing','Quotes','To Do 
Items','Employee','Exit']
    calls = [clientsmenu, jobsmenu, billingmenu, quotesmenu,
todomenu, empmenu, quit]
    n = display_menu(menu)
    calls[n]()


And similarly for your other menus:

def secondmenu():
    menu = ['About','Help','Exit']
    calls = [aboutmenu, helpmenu, quit]
    n = display_menu(menu)
    calls[n]()




> something like sysctl variables in Linux perhaps but in this case
> only valid for this program.
>
> Its clear from the responses that this solution is not available in
> python, I wish it were, it would make my life much easier for this
> project.

No, you only *think* it would make your life easier. This is probably 
the time to quote Yoda's speech about the Dark Side of the Force 
from "The Empire Strikes Back".

Such global settings are "easier, faster, simpler"... for about fifteen 
minutes. The right solution is to build reusable building blocks, then 
put them together.


[...]
> Lie also referred to my particular case as a valid exception, are
> there enough other such valid exceptions that requesting a feature
> enhancement would gain some traction?

Not a hope in hell.

You have misunderstood Lie's comment. He's talking about the use of an 
index *at all*. Normally in Python you shouldn't need to use indexes, 
regardless of whether they start with 0 or 1 or 3.1425.... Your example 
of a text menu is an exception to the rule (more of a guideline 
really) "you shouldn't care about indexes".



-- 
Steven D'Aprano