python遍历列表一直回到选择的元素

Question

loop a list past the last element back to the first

lets say i picked element 2 in a 4 element list. How can i then loop through the whole list back to element 2. I have tried -1, -i, 1-i, i-1 but the list never goes back to element 0 just stops at the last one. eg

rand_list = ["750", "500", "255", "1000"]`
for i in range(len(rand_list)):
    print(rand_list[i:X])

in this what would i put in place of X i would want the print to be 750 500 255 1000 then 500 255 1000 750 then 255 1000 750 500 etc.

Answer 1

Just slice the list twice and concatenate the results:

>>> for i in range(len(rand_list)):
...     print(rand_list[i:] + rand_list[:i])
... 
['750', '500', '255', '1000']
['500', '255', '1000', '750']
['255', '1000', '750', '500']
['1000', '750', '500', '255']

Answer 2

This could work : Creating a list of index with the order you like.

rand_list = ["750", "500", "255", "1000"]
index = 2

for i in range(index, len(rand_list))+range(index) :
    print "index : {}, value : {}".format(i, rand_list[i])

It will output :

index : 2, value : 255
index : 3, value : 1000
index : 0, value : 750
index : 1, value : 500

Also, if you want to test all cases, you can update index with a loop from values of range(len(rand_list)) .