caterpillar created by vetional - https://repl.it/MPFx/1

main.py

def caterpillarMethod(A, s):
  n = len(A)
  front, total = 0, 0
  
  for back in xrange(n):
    print "back: ",back
    while (front < n and total + A[front] <= s):
      total += A[front]
      front += 1
      print "total:", total, "back:", back, "front:",front
    if total == s:
      return True
  
    total -= A[back]
  
  return False
  
  
A = [6, 2, 7, 4, 1, 3, 6]
print caterpillarMethod(A,12)