Why does range(start, end) not include end?

Question

>>> range(1,11)

gives you

[1,2,3,4,5,6,7,8,9,10]

Why not 1-11?

Did they just decide to do it like that at random or does it have some value I am not seeing?

Answer 1

Because it's more common to call range(0, 10) which returns [0,1,2,3,4,5,6,7,8,9] which contains 10 elements which equals len(range(0, 10)). Remember that programmers prefer 0-based indexing.

Also, consider the following common code snippet:

for i in range(len(li)):
    pass

Could you see that if range() went up to exactly len(li) that this would be problematic? The programmer would need to explicitly subtract 1. This also follows the common trend of programmers preferring for(int i = 0; i < 10; i++) over for(int i = 0; i <= 9; i++).

If you are calling range with a start of 1 frequently, you might want to define your own function:

>>> def range1(start, end):
...     return range(start, end+1)
...
>>> range1(1, 10)
[1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

Answer 2

The length of the range is the top value minus the bottom value.

It's very similar to something like:

for (var i = 1; i < 11; i++) {
    //i goes from 1 to 10 in here
}

in a C-style language.

Also like Ruby's range:

1...11 #this is a range from 1 to 10

However, Ruby recognises that many times you'll want to include the terminal value and offers the alternative syntax:

1..10 #this is also a range from 1 to 10