Regroup list elements to generate new lists of 2 pairs

Do you actually want this output?

lstGroup2{1}.attr1 = b1

lstGroup2{1}.attr2 = b2

lstGroup2{1}.attr3 = b3

lstGroup2{2}.attr1 = c1

lstGroup2{2}.attr2 = c2

lstGroup2{2}.attr3 = c3

or this?

lstGroup2{0}.attr1 = b1

lstGroup2{0}.attr2 = b2

lstGroup2{0}.attr3 = b3

lstGroup2{1}.attr1 = c1

lstGroup2{1}.attr2 = c2

lstGroup2{1}.attr3 = c3

oh thanks for the hint @egomm..you're right as the index for the new list will start at 0 , I'll edit the output example..

What is the intention afterwards? It's fairly straightforward to build the list you want in python but you would have to type in all the lstGroup names to expose them. 

import fme
import fmeobjects

def processFeature(feature):
        attr1 = feature.getAttribute('mylist{}.attr1')
        attr2 = feature.getAttribute('mylist{}.attr2')
        attr3 = feature.getAttribute('mylist{}.attr3')
        for i, val in enumerate(attr1):
            if i < len(attr1)-1:
                feature.setAttribute('lstGroup'+str(i+1)+'{0}.attr1',attr1[i])
                feature.setAttribute('lstGroup'+str(i+1)+'{1}.attr1',attr1[i+1])
                feature.setAttribute('lstGroup'+str(i+1)+'{0}.attr2',attr2[i])
                feature.setAttribute('lstGroup'+str(i+1)+'{1}.attr2',attr2[i+1])
                feature.setAttribute('lstGroup'+str(i+1)+'{0}.attr3',attr3[i])
                feature.setAttribute('lstGroup'+str(i+1)+'{1}.attr3',attr3[i+1])

import fme
import fmeobjects

def processFeature(feature):
        attr1 = feature.getAttribute('mylist{}.attr1')
        attr2 = feature.getAttribute('mylist{}.attr2')
        attr3 = feature.getAttribute('mylist{}.attr3')
        for i, val in enumerate(attr1):
            if i < len(attr1)-1:
                feature.setAttribute('lstGroup'+str(i+1)+'{0}.attr1',attr1[i])
                feature.setAttribute('lstGroup'+str(i+1)+'{1}.attr1',attr1[i+1])
                feature.setAttribute('lstGroup'+str(i+1)+'{0}.attr2',attr2[i])
                feature.setAttribute('lstGroup'+str(i+1)+'{1}.attr2',attr2[i+1])
                feature.setAttribute('lstGroup'+str(i+1)+'{0}.attr3',attr3[i])
                feature.setAttribute('lstGroup'+str(i+1)+'{1}.attr3',attr3[i+1])

many thanks!..the big challenge is I found the original list can be varied in length.. so it could be 4 elements or 50+ in some cases (dynamic list length), so the grouping should accommodate the list length.