arr = [4,3,2,1]
n = len(arr)
for i in range(0, n-1):  # 如果n=0,1;range输出空表格,不进行for循环
    print('第{}遍'.format(i+1))
    for j in range(1, n-i):
        if arr[j-1] > arr[j]:
            arr[j-1], arr[j] = arr[j], arr[j-1]
arr

arr = [4,3,2,1]
n = len(arr)
for i in range(0, n-1):  # 如果n=0,1;range输出空表格,不进行for循环
    print('第{}遍'.format(i+1))
    for j in range(0, n-1-i):
        if arr[j] > arr[j+1]:
            arr[j], arr[j+1] = arr[j+1], arr[j]
arr