Slicing [N::-1]

[Gary Herron]

Mensanator wrote:
> On Mar 5, 3:42 pm, Gary Herron <gher... at islandtraining.com> wrote:
>   
>> Mensanator wrote:
>>
>>     
>>> The only way to get a 0 from a reverse range() is to have a bound of
>>> -1.
>>>       
>> Not quite.  An empty second bound goes all the way to the zero index:
>>     
>
> Not the same thing. You're using the bounds of the slice index.
> I was refering to the bounds of the range() function.
>
>   
>>>> for a in range(9,-9,-1):print(a,end=' ')
>>>>         
> 9 8 7 6 5 4 3 2 1 0 -1 -2 -3 -4 -5 -6 -7 -8
>
> To get that to stop at 0, you use a -1 as the bounds:
>
>   
>>>> for a in range(9,-1,-1):print(a,end=' ')
>>>>         
> 9 8 7 6 5 4 3 2 1 0
>
> Your slice notation only works if the last (first?) number in
> the range happens to be 0. What if the range bounds were variables?
> You may still want to force the range's last number to be 0 by
> using a constant like range(a,-1,-1) rather than just take
> the last number of range(a,b,-1) by using slice notation.
>   

All true  and valid of course, but I was just contridicting the "the 
ONLY way to get a 0" (emphasis mine) part of the statement.

Gary Herron



>   
>>  >>> range(9)[2::-1]
>> [2, 1, 0]
>>
>> Gary Herron
>>