def trimAlphaNum(value):
  """
  工具方法，去掉字符串开头和结尾的字母数字
  """
  while value and value[-1].isalnum():
    value = value[:-1]
  while value and value[0].isalnum():
    value = value[1:]

  return value

def findDynamicContent(firstPage, secondPage):
  """
  寻找页面中的动态内容
  """
  DYNAMICITY_MARK_LENGTH = 32
  if not firstPage or not secondPage:
    return
  blocks = difflib.SequenceMatcher(None, firstPage, secondPage).get_matching_blocks()
  dynamicMarkings = []

    # Removing too small matching blocks
  for block in blocks[:]:
    (_, _, length) = block

    if length <= DYNAMICITY_MARK_LENGTH:
      blocks.remove(block)

    # Making of dynamic markings based on prefix/suffix principle
  if len(blocks) > 0:
    blocks.insert(0, None)
    blocks.append(None)

    for i in xrange(len(blocks) - 1):
      prefix = firstPage[blocks[i][0]:blocks[i][0] + blocks[i][2]] if blocks[i] else None
      suffix = firstPage[blocks[i + 1][0]:blocks[i + 1][0] + blocks[i + 1][2]] if blocks[i + 1] else None

      if prefix is None and blocks[i + 1][0] == 0:
        continue

      if suffix is None and (blocks[i][0] + blocks[i][2] >= len(firstPage)):
        continue

      prefix = trimAlphaNum(prefix)
      suffix = trimAlphaNum(suffix)

      dynamicMarkings.append((prefix[-DYNAMICITY_MARK_LENGTH / 2:] if prefix else None, suffix[:DYNAMICITY_MARK_LENGTH / 2] if suffix else None))

  if len(dynamicMarkings) > 0:
    return dynamicMarkings

def removeDynamicContent(page, dynamicMarkings):
  """
  去掉页面中的动态内容
  """
  if page:
    for item in dynamicMarkings:
      prefix, suffix = item

      if prefix is None and suffix is None:
        continue
      elif prefix is None:
        page = re.sub(r'(?s)^.+%s' % re.escape(suffix), suffix.replace('\\', r'\\'), page)
      elif suffix is None:
        page = re.sub(r'(?s)%s.+$' % re.escape(prefix), prefix.replace('\\', r'\\'), page)
      else:
        page = re.sub(r'(?s)%s.+%s' % (re.escape(prefix), re.escape(suffix)), '%s%s' % (prefix.replace('\\', r'\\'), suffix.replace('\\', r'\\')), page)
  return page

def demo():
  # page1
  a = """56f231816b288<br/>1||admin||admin<br/>"""

  # page2
  b = """56f2318735582<br/>1||admin||admin<br/>"""
  # 对动态内容进行标记
  dynamicMarkings = findDynamicContent(a, b)
  # 获取去掉动态内容之后的页面
  print removeDynamicContent(a, dynamicMarkings)