new_contents: #!/usr/bin/python -e
  # -*- encoding: utf-8 -*-
  #
  # Copyright (c) 2013 ASMlover. All rights reserved.
  #
  # Redistribution and use in source and binary forms, with or without
  # modification, are permitted provided that the following conditions
  # are met:
  #
  #  * Redistributions of source code must retain the above copyright
  #    notice, this list ofconditions and the following disclaimer.
  #
  #  * Redistributions in binary form must reproduce the above copyright
  #    notice, this list of conditions and the following disclaimer in
  #    the documentation and/or other materialsprovided with the
  #    distribution.
  #
  # THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
  # "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
  # LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
  # FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
  # COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
  # INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
  # BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
  # LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
  # CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  # LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
  # ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
  # POSSIBILITY OF SUCH DAMAGE.
  
  class List(object):
    class ListNode(object):
      def __init__(self):
        self.prev = None
        self.next = None 
        self.data = None 
      def __del__(self):
        self.prev = None
        self.next = None
        self.data = None 
  
    def __init__(self):
      self.head_ = self.ListNode()
      self.head_.prev = self.head_ 
      self.head_.next = self.head_
      self.size_ = 0 
      self.iter_ = None
   
    def __del__(self):
      self.clear()
      self.iter_ = None 
   
    def __iter__(self):
      self.iter_ = self.begin()
      return self
  
    def next(self):
      if self.iter_ == self.end():
        raise StopIteration
      else:
        data = self.iter_.data 
        self.iter_ = self.iter_.next
        return data
  
    def clear(self):
      it = self.begin()
      while it != self.end():
        node = it 
        it = it.next 
        self.erase(node)
      self.head_.prev = self.head_
      self.head_.next = self.head_
      self.size_ = 0
  
    def empty(self):
      return self.begin() == self.end()
  
    def size(self):
      return self.size_ 
  
    def insert(self, pos, x):
      node = self.ListNode()
      node.data = x 
      node.prev = pos.prev
      node.next = pos 
      pos.prev.next = node 
      pos.prev = node 
  
      self.size_ += 1 
  
    def erase(self, pos):
      prev = pos.prev 
      next = pos.next 
      prev.next = next 
      next.prev = prev 
      del pos 
  
      self.size_ -= 1
   
    def begin(self):
      return self.head_.next
  
    def end(self):
      return self.head_
    
    def push_front(self, x):
      self.insert(self.begin(), x)
  
    def push_back(self, x):
      self.insert(self.end(), x) 
  
    def pop_front(self):
      assert self.begin() != self.end()
      self.erase(self.front())
    
    def pop_back(self):
      assert self.begin() != self.end()
      pos = self.end()
      self.erase(pos.prev)
    
    def front(self):
      assert self.begin() != self.end()
      return self.begin().data
  
    def back(self):
      assert self.begin() != self.end()
      return self.end().prev.data 
  
subject: add list module for mini-stl (Python)