python for loop

Steven D'Aprano steve at REMOVE-THIS-cybersource.com.au
Wed Apr 1 14:34:44 CEST 2009


On Wed, 01 Apr 2009 04:39:39 -0700, bearophileHUGS wrote:

> Lada Kugis:
>> (you have 1 apple, you start counting from 1 ...<
> 
> To little children I now show how to count starting from zero: apple
> number zero, apple number one, etc, and they find it natural enough :-)


Ah, but that's not the same as counting ordinals from zero. Consider the 
difference between an empty list, which has zero items, and a list of 
length one, which as that item in position zero.

The empty list [] clearly has zero items, in zero "bins", so the bins 
aren't numbered.

A list with one item [x] has one bin, labelled "Index 0".
A list with two items [x, y] has two bins, labelled Index 0 and Index 1.
A list with three items [x, y, z] has three bins, labelled Index 0, Index 
1 and Index 2.
etc.

Counting "No apples plus one apple makes one apple" is easy enough. But 
pointing to an apple clearly there and saying "Let's call that apple 
number zero, even though there is one apple", that requires a very 
special child!


-- 
Steven



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