what is [::-1] in python

Question

explain about the above declaration in python

Answer 1

It is a slice operator, which somehow reverses any ordered iterables.

Answer 2

First try to understand this code:

x=[0,1,2,3,4,5]

#using ":" will print everything
print( x[ : ] ) >>>[0,1,2,3,4,5]

#if we want to step 2 numbers we can use third argument as
print( x[ 0 : 5 : 2 ] ) >>>[0,2,4]

#if we want to start from back we write in the same way but with "-" sign (note: from back the index of 1st digit is -1 not 0
print( x[ -1 : -5 : -2] ) >>>[5,3,1]

#now if we want to to print everything without giving indices of 1st two arguments we can use ":" as described earlier(here we used two colons to skip middle argument and include the 3rd argument)
print( x[ : : -2] ) >>>[4,2,0]

#and if we don't want to skip we can write as
print( x[ : : -1] ) >>>[5,4,3,2,1,0]

I hope now you have understood the reversing of list.