Interpolation search missing condition? about 40-algorithms-every-programmer-should-know HOT 1 OPEN

def IntPolsearch(list,x ):
   idx0 = 0
   idxn = len(list) - 1
   while idx0 <= idxn and (list[idx0] <= x <= list[idxn]):
      # Find the mid point
      mid = idx0 + int(((float(idxn - idx0)/( list[idxn] - list[idx0])) *( x - list[idx0])))
      # Compare the value at mid point with search value
      if list[mid] == x:
         return True
      if list[mid] < x:
         idx0 = mid + 1
      else:
         idxn = mid - 1
   return False