old_contents: __author__ = 'Chengyu'
  import datetime
  
  
  def user_key_gen(uid, region_num, phone_num, datetime):
      key = 'a'
      return key
  
  
  def message_key_gen(sender_uid, receiver_uid, datetime):
      key = 'b'
      return key
new_contents: # -*- coding:utf-8 -*-
  __author__ = 'Chengyu'
  import hashlib
  
  
  def user_key_gen(uid, region_num, phone_num, datetime):
      key = str(uid) + str(region_num) + str(phone_num) + str(datetime)
      key = hashlib.new("md5", key).hexdigest()
      return key
  
  
  def message_key_gen(sender_uid, receiver_uid, datetime):
      key = str(sender_uid) + str(receiver_uid) + str(datetime)
      key = hashlib.new("md5", key).hexdigest()
      return key
subject: add hash