How to create an array list like a circle / loop?

Question

i have an array list, i find a point in the list i require and then take 3 values from that point right, however while this works perfect, i am worried due that if the value was the last value in the list it would error, instead i would want it to loop around to the start of the list again

for example if it picked z i would then want it to also pick a and b as well

this is my current code :

descriptor_position = bisect_left(orHashList, b32decode(descriptor_id,1)) #should be identiy list not HSDir_List #TODO - Add the other part of the list to it so it makes a circle
   for i in range(0,3):
      responsible_HSDirs.append(orHashList[descriptor_position+i])
   return (map(lambda x: consensus.get_router_by_hash(x) ,responsible_HSDirs))

what function or library can i use that achieves this ?

Thanks

DNA · Accepted Answer · 2014-07-18 21:29:02Z

4

You can generate the indices you want using a range, then wrap the indices round to the start of a list using the modulus % operator within a list comprehension - something like:

>>> a = ['a', 'b', 'c', 'd', 'e']
>>> index = 4
>>> [x % len(a) for x in range(index, index+3)]

[4, 0, 1]

>>> [a[x % len(a)] for x in range(index, index+3)]

['e', 'a', 'b']

answered Jul 18, 2014 at 21:29

DNA

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