Guys please explain the print part of each

Question

squares = [0, 1, 4, 9, 16, 25, 36, 49, 64, 81]
print(squares[-1:4:1])

squares = [0, 1, 4, 9, 16, 25, 36, 49, 64, 81]
print(squares[-1:4:-1])
#is it possible to have -4 for the step part? is yes how does it work?

Answer 1

Coder

squares[start:stop:step]

for print(squares[-1:4:-4])

here,
start = -1
stop = 4
step = -4

+----+----+----+----+----+----+----+----+----+----+
| 0 | 1 | 4 | 9 | 16 | 25| 36 | 49 | 64 | 81|
+----+----+----+----+----+----+----+----+----+----+
0 1 2 3 4 5 6 7 8 9
-10 -9 -8 -7 -6 -5 -4 -3 -2 -1
^ ^
| |
stop start

So we can see from the figure above S is at 81 and E is at 16.
1) squares[start] => squares[-1] is printed which is 81
2) squares[start+step] => squares[-1+(-4)] = squares[-5] is printed which is 25

Hence, we have
[81, 25]

Answer 2

https://stackoverflow.com/questions/509211/understanding-slice-notation

a[-1] # last item in the array
a[-2:] # last two items in the array
a[:-2] # everything except the last two items

Similarly, step may be a negative number:

a[::-1] # all items in the array, reversed
a[1::-1] # the first two items, reversed
a[:-3:-1] # the last two items, reversed
a[-3::-1] # everything except the last two items, reversed

here's a code, if you still don't understand let me know.
https://code.sololearn.com/cAQBZ3dHmbKW/?ref=app

Answer 3

-1 is the first number from the end to the first and -4 is the fourth number from the end to the first. But when we write [-1: -4] the number four does not count and the number before it counts. And if we put the third number in the bracket [ -1: -4: -1] the numbers are one by one Prints from end to first.

Answer 4

coder This is the method of cutting lists and listing indexes that rkk has explained to you

Answer 5

Or print(squares[-1:-6:-4])
Good luck ;)))

Answer 6

i know it's slice list but when i made my own examples i found there is no rules for the bounds. It depends on example. I don't understand the negative bounds mixed with positive bounds.

Answer 7

thx for your answers.
how about this? which prints [81, 25]
print(squares[-1:4:-4])
^