A=[1,2,3,4,5,6] print(A[2:5:-1]) output is [ ]

Question

why is output empty list and what does -1 Do their

Answer 1

The output will be [].

The syntax is [start:stop:step]. A negative step makes it count backwards, so start has to be bigger than stop in this case.

With a[2:5:-1], you're telling python to count upwards (from index 2 to index 4) in steps of -1. That won't work.

a[5:2:-1] would work and the output would be [6, 5, 4].

Note that the end index is never included.