Can someone please explain what "r[ i ]" and " r[~i] " mean in this solution?
# Python3 program to print diagonals in 2D list
def printDiagnol(lst):
# To print Primary Diagnol
print('Diagnol 1 - ', end ="")
print([r[i] for i, r in enumerate(lst)]) # what is r[i]?
# To print Secondary Diagnol
print('Diagnol 2 - ', end ="")
print([r[~i] for i, r in enumerate(lst)])# what is r[~i]?
# Driver code
lst = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]
printDiagnol(lst)
enumerate.