why it outputs [7], please explain this code!...

Question

numbers=[1,2,3,4,5,6,7,9,9]
print(numbers[6:2:-4])

output:
[7]

Answer 1

Sujithra Focus here :
In list[start:end:stepsize]

start is always inclusive.
end is always exclusive.

For example ,
numbers=[1,2,3,4,5,6,7,9,9]
print(numbers[6:2:-4])

#numbers[6]=7 (ALWAYS INCLUSIVE NO MATTER WHAT YOUR STEP SIZE IS)

#numbers[2]= 3(ALWAYS EXCLUSIVE IT WILL NEVER INCLUDED)

Here output will be [7 ] because it will include start which is 7 and then follow steps from back and then it will not print 3 because it is exclusive.

Try this:

numbers=[1,2,3,4,5,6,7,9,9]
print(numbers[6:0:-4])
print(numbers[0:6:4])
and u will understand better.

Answer 2

Thank you sarada lakshmi and Slick

Answer 3

Thank you so much DEVIL

Answer 4

Okay so broken down:

numbers[6] = 7
numbers[2] = 3

In "numbers[6:2:-4]" the "-4" means two things:
-first, the (-) tells you to reverse the list order.
-then the (4) tells you that you will be counting every 4th number in the list.

So just for an example:
numbers[6:2:-1]
[7, 6, 5, 4]

Keep in mind the 3 is not included because the list operation " list[x:y:z] " takes every number including x and up until but not including y. z is the "step"

Since (-4) is the third parameter instead of -1 like the example above, the next number to be shown in the list is 3. But since 3 is not included...

[7] is your output.

Answer 5

I think it's not good approach.. Coz, its a simple list, it's okay.. What if you take a large sized list.. Suppose having size 1000 or more... Always try to write code that satisfy each and every input you take...

Answer 6

sarada lakshmi very true, this will only work with a handful of cases. What I believe the poster was trying to understand is the output. No use writing amazing functions when you don't understand how they work.