Why does first list has one less element in the same range?

Question

https://www.sololearn.com/en/compiler-playground/caT4cbimkq5J

Answer 1

It is because:
range(15), if put it into a list, becomes [0, 1, 2, ... 14] # 15 elements
range(1, 15), if put it into a list, becomes [1, 2, 3, ... 14] # 14 elements

Answer 2

Igor Matić ,

as Wong Hei Ming already said, but with other words:

> if we use only 1 argument with range() function, this argument is seen as the upper bound, the lower bound is 0 by default.

> if we use 2 arguments, lower and upper bounds are like the arguments given.

> in both cases the upper bound itself is *not* included in the result. so if we need numbers from 0 upto and including 10 we have to do it like:

print(list(range(0, 10 +1)))

or:

print(list(range(10 +1)))

Answer 3

Wong Hei Ming ,

thanks for your great explanation! very well done!

Answer 4

A little something add to Lothar's answer.

> if we use 3 arguments, you can increase / decrease the next value by more than 1
print(list(range(1, 15, 3)))
# [1, 4, 7, 10, 13]
print(list(range(15, 1, -3)))
# [15, 12, 9, 6, 3]

So, the range function can be rewritten as:
range(start=0 (optional), end (required), step (optional))

When you type range(15), it is translated into range(0, 15). The first number is 0 and end at 15 (exclusive).
If you type range(1, 15), the first number is 1, and end at 15 (exclusive).

Answer 5

Igor Matić
Short answer: yes

Medium answer: why not trying it in playground?

Long answer: remember range(start, end, step).

If we want a descending order, the start must be the higher end, and end is the lower end.
If you type:
# thinking like: yeah, we start from 15, end at 1, and the step size is 3
print(list(range(15, 1, 3)))
what you get: [] # an empty list

It is because the stepping is a positive number.
We start from 15, step is positive 3 so the next number is 18.
However the end is 1, so it must be descending. Which mean the next number must be smaller than 15.

So you can think range() function works like this:
From the "start", we ADD the "step" until reaching the "end".
So in the previous answer: print(list(range(15, 1, -3)))
The first number: 15
The second number: 15 + (-3) = 12
The third number: 12 + (-3) = 9
And so on...

Answer 6

Thank you!

Answer 7

Wong Hei Ming , for ranges in descending order, arguments must be reversed (from big to small number) and stepping needs to be a negative number?