1. reversed()

a = [1,2,3,4]
for i in reversed(a):
    print(i)

2. range(len(a)-1,-1,-1)

a = [1,4]
for i in range(len(a)-1,-1):
    print(a[i])

3. range(len(a)) + ~操作符

~按位取反运算符：对数据的每个二进制位取反,即把1变为0,把0变为1 。~x 类似于 -x-1

a = [1,4]
for i in range(len(a)):
    print(a[~i])

4. slice

缺点是slice是浅复制，需要额外的空间

a = [1,4]
for i in a[::-1]:
    print(i)

5. length-i-1

a = [1,4]

seq_length = len(a)
for i in range(seq_length):
    print(a[seq_length-i-1])