python - 枚举函数的Python解释

Question

有人可以解释一下这个解决方案中的“r[i]”和“r[~i]”是什么意思吗？

# 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) 

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