Python-Flask: 引用错误：弱引用对象不再存在

Question

我在用 Python 的 Flask 框架。我写了这段代码：

from flask import *
import mysql.connector
def connect_db():   
        db = mysql.connector.Connect(host='***',user='***',password='**',database='***')
        return db.cursor()

def query_db(query, args=(), one=False):
    cur = g.db  
    cur.execute(query, args)
    rv = [dict((cur.description[idx][0], value)
    for idx, value in enumerate(row)) for row in cur.fetchall()]
    return (rv[0] if rv else None) if one else rv

    @app.before_request
    def before_request():
        g.db = connect_db()
        blogOptions = query_db('select * from tbl_options',None)    

    @app.route("/")
    def index():    
        return render("index.html")

当我运行这段代码时，它显示了

ReferenceError: weakly-referenced object no longer exists

并且有错误追踪信息：

Traceback (most recent call last):
  File "/Users/ozcan/Documents/python/venv/lib/python2.7/site-packages/flask/app.py", line 1701, in __call__
    return self.wsgi_app(environ, start_response)
  File "/Users/ozcan/Documents/python/venv/lib/python2.7/site-packages/flask/app.py", line 1689, in wsgi_app
    response = self.make_response(self.handle_exception(e))
  File "/Users/ozcan/Documents/python/venv/lib/python2.7/site-packages/flask/app.py", line 1687, in wsgi_app
    response = self.full_dispatch_request()
  File "/Users/ozcan/Documents/python/venv/lib/python2.7/site-packages/flask/app.py", line 1360, in full_dispatch_request
    rv = self.handle_user_exception(e)
  File "/Users/ozcan/Documents/python/venv/lib/python2.7/site-packages/flask/app.py", line 1356, in full_dispatch_request
    rv = self.preprocess_request()
  File "/Users/ozcan/Documents/python/venv/lib/python2.7/site-packages/flask/app.py", line 1539, in preprocess_request
    rv = func()
  File "/Users/ozcan/Documents/python/app.py", line 124, in before_request
    blogOptions = query_db('select * from tbl_options',None)
  File "/Users/ozcan/Documents/python/app.py", line 47, in query_db
    cur.execute(query, args)
  File "/Users/ozcan/Documents/python/venv/lib/python2.7/site-packages/mysql/connector/cursor.py", line 364, in execute
    if self._have_unread_result():
  File "/Users/ozcan/Documents/python/venv/lib/python2.7/site-packages/mysql/connector/cursor.py", line 193, in _have_unread_result
    return self._connection.unread_result
ReferenceError: weakly-referenced object no longer exists

我该怎么解决这个问题呢？

Answer 1

你在这里创建的连接对象，在函数结束时会被垃圾回收机制清理掉，这样当游标后面再去引用它时，它就不存在了：

def connect_db():   
        db = mysql.connector.Connect(host='***',user='***',password='**',database='***')
        return db.cursor()

你可以把它返回，或者存储在 g 里，这样它就可以在请求的整个过程中一直存在。