Time travel - how to simplify?

[Peter Otten]

Andrew Z wrote:

> well, yeah, it's unidirectional and final destination is always the same
> and have little to do with the question.
> 
> Say, i have a dict:
> 
> fut_suffix ={ 1 : 'F',
>               2 : 'G',
>               3 : 'H',
>               4 : 'J',
>               5 : 'K',
>               6 : 'M',
>               7 : 'N',
>               8 : 'Q',
>               9 : 'U',
>               10: 'V',
>               11: 'X',
>               12: 'Z'
>               }
> 
> where key is a month.
> Now i want to get certain number of months. Say, i need  3 months duration
> starting from any month in dict.
> 
> so if i start @ 7th:
> my_choice =7
>  for mnth, value in fut_suffix:
>     if my_choice >= mnth
>        # life is great
> but if :
> my_choice = 12 then my "time travel" becomes pain in the neck..
> 
> And as such - the question is - what is the smart way to deal with cases
> like this?

Make a lookup list that is big enough for your application and then use 
slicing:

>>> def months(first, count, lookup=list("FGHJKMNQUVXZ" * 3)):
...     start = first - 1
...     return lookup[start: start + count]
... 
>>> months(3, 3)
['H', 'J', 'K']
>>> months(12, 3)
['Z', 'F', 'G']