Slice a list including two items before and two items after specified item with wrap around?

Question

I've got a dictionary with integer keys and list values. I want to be able to iterate through the list and if I find an entry that matches my input I want to print/store the two items before the specified, the specified, and the two items after, thus storing a new list of five. I am wanting this to wrap around so that if the match were the last in the list it would get the last three of the list and the first two in the list. I can't figure it out.

strings = {1:['e','f','fsharp','g','gsharp','a','asharp','b','c','csharp','d','dsharp'],
       2:['a','asharp','b','c','csharp','d','dsharp','e','f','fsharp','g','gsharp'],
       3:['d','dsharp','e','f','fsharp','g','gsharp','a','asharp','b','c','csharp'],
       4:['g','gsharp','a','asharp','b','c','csharp','d','dsharp','e','f','fsharp'],
       5:['b','c','csharp','d','dsharp','e','f','fsharp','g','gsharp','a','asharp'],
       6:['e','f','fsharp','g','gsharp','a','asharp','b','c','csharp','d','dsharp']}

usr_note = input("Enter note: ")

surrounding_notes = strings[1][strings[1].index(usr_note)-2:strings[1].index(usr_note)+2]

I think this question (& answer) is more on topic, actually: http://stackoverflow.com/questions/4528740/wrapping-around-a-python-list-as-a-slice-operation ; particular the suggestion to use `collections.deque`. The duplicate question considers only simple (1 element) indexing, not slicing. — , Feb 14 '16 at 05:38

Martín Muñoz del Río · Accepted Answer · 2016-02-14T05:36:23.770

Try:

def surroundings(st,i):
    if i<2:
        return st[i-2:] + st[:i+3]
    if i+2 >= len(st):
        return st[i-2:] + st[:i+3-len(st)]

    return st[i-2:i+3]

usr_note = 'f'
i = strings[1].index(usr_note)
surrounding_notes = surroundings(strings[1], i)
print surrounding_notes

usr_note = 'd'
i = strings[1].index(usr_note)
surrounding_notes = surroundings(strings[1], i)
print surrounding_notes

usr_note = 'c'
i = strings[1].index(usr_note)
surrounding_notes = surroundings(strings[1], i)
print surrounding_notes

Slice a list including two items before and two items after specified item with wrap around?

1 Answers1