160 intersection of two linked lists

def (self, headA, headB):
  """w
  :type head1, head1: ListNode
  :rtype: ListNode
  """
  if headA == None or headB == None:
      return None
  countA = 0
  countB = 0
  pa = headA
  pb = headB
  while pa !=None:
      pa = pa.next
      countA+=1
  while pb != None:
      pb = pb.next
      countB+=1
  if pa != pb:
    return None
  paa = headA
  pbb = headB
  lengthDiff = max(countA,countB) - min(countA,countB)
  if countA < countB:
      countx = 0
      while countx < lengthDiff and pbb != None:
          pbb = pbb.next
          countx+=1
  elif countA > countB:
      countx = 0
      while countx < lengthDiff and paa != None:
          paa = paa.next
          countx+=1
  while paa != None and pbb != None:
      if paa.val == pbb.val:
          return paa
      paa = paa.next
      pbb = pbb.next
  return None