Pyscopg DB - 错误为代码添加持久性

我正在研究Udacity的在线项目.我正在使用vagrant他们配置,运行包含数据库的服务器.不幸的是,当我试图给出代码持久性时,服务器每次都会返回一个错误.我是python的新手所以请原谅任何明显的错误.

这是错误:

Serving HTTP on port 8000...
Traceback (most recent call last):
  File "/usr/lib/python2.7/wsgiref/handlers.py", line 85, in run
    self.result = application(self.environ, self.start_response)
  File "forum.py", line 95, in Dispatcher
    return DISPATCH[page](env, resp)
  File "forum.py", line 68, in Post
    length = int(env.get('CONTENT_LENGTH', 0))
ValueError: invalid literal for int() with base 10: ''
10.0.2.2 - - [06/Jan/2016 04:44:16] "GET /post HTTP/1.1" 500 59
10.0.2.2 - - [06/Jan/2016 04:44:16] "GET /favicon.ico HTTP/1.1" 404 22

这是我在forumdb.py中更改的代码:

#
# Database access functions for the web forum.
# 

import psycopg2

## Database connection

def GetAllPosts():
    DB = psycopg2.connect("dbname=forum")
    c = DB.cursor()
    c.execute("SELECT time, content FROM posts ORDER BY time DESC")
    posts = ({'content': str(row[1]), 'time': str(row[0])}
             for row in c.fetchall())

    # This returns a dictionary -- returning just c.fetchall() will return a list of tuples

    DB.close()
    return posts

def AddPost(content):
    DB = psycopg2.connect("dbname=forum")
    c = DB.cursor()
    c.execute("INSERT INTO posts (content) values ('%s')" % content)
    DB.commit()
    DB.close()

forum.py - 此文件呈现html从数据库中提取数据:http://pastebin.com/ZiHWiiwr

请帮忙 !