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 lik

Answer 1

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

Answer 2

Consider the code

for i in range(10):
    print "You'll see this 10 times", i

The idea is that you get a list of length y-x, which you can (as you see above) iterate over.

Read up on the python docs for range - they consider for-loop iteration the primary usecase.

Answer 3

It works well in combination with zero-based indexing and len(). For example, if you have 10 items in a list x, they are numbered 0-9. range(len(x)) gives you 0-9.

Of course, people will tell you it's more Pythonic to do for item in x or for index, item in enumerate(x) rather than for i in range(len(x)).

Slicing works that way too: foo[1:4] is items 1-3 of foo (keeping in mind that item 1 is actually the second item due to the zero-based indexing). For consistency, they should both work the same way.

I think of it as: "the first number you want, followed by the first number you don't want." If you want 1-10, the first number you don't want is 11, so it's range(1, 11).

If it becomes cumbersome in a particular application, it's easy enough to write a little helper function that adds 1 to the ending index and calls range().