Python 和 SQLite : Check if an item exists in a database?

Question

我有一种方法可以将希望注册的用户的用户名和密码写入数据库。在将他们提供的用户名和密码存储到数据库之前，我想检查他们选择的用户名是否已经存在于“待定”列表或已批准的“联系人”列表中。

这是我用来执行此操作的代码:

@cherrypy.expose
def writePending(self, username=None, password=None, message=None, signin=None):
    """ Add request of friendship into a database which stores all
        pending friendships.
    """

    page = get_file(staticfolder + "/html/friendingPage.html")

    if username != "" and password != "" and message !="":
        con = lite.connect('static/database/Friendship.db')
        cur = con.cursor()

        with con:      
            cur.execute("CREATE TABLE IF NOT EXISTS pending(user TEXT, pass TEXT, info TEXT)")
            cur.execute("CREATE TABLE IF NOT EXISTS contacts(user TEXT, pass TEXT)")

            "Check to see if the username is already registered"

            cur.execute("Select * from pending where user = ?", (username, ))
            check1=cur.fetchone()
            cur.execute("Select * from contacts where user = ?", (username, ))
            check2=cur.fetchone()

            if check1[0] != None:
                page = page.replace("$Error", "The ID you used is still pending for friendship")
            elif check2[0] != None:
                page = page.replace("$Error", "The ID you used is already added as a contact")
            else:
                cur.execute("CREATE TABLE IF NOT EXISTS pending(user TEXT, pass TEXT, info TEXT)")   
                cur.execute("INSERT INTO pending VALUES(?, ?, ?)", (username, password, message))               
                page = get_file(staticfolder + "/html/thankYouPage.html")

    else:
        page = get_file(staticfolder + "/html/friendingPage.html")
        page = page.replace("$Error", "You Must fill out all fields to proceed")

    return page

但是，我会收到一条消息

Traceback (most recent call last):
  File "/usr/lib/pymodules/python2.7/cherrypy/_cprequest.py", line 606, in respond
    cherrypy.response.body = self.handler()
  File "/usr/lib/pymodules/python2.7/cherrypy/_cpdispatch.py", line 25, in __call__
    return self.callable(*self.args, **self.kwargs)
  File "proj1base.py", line 540, in writePending
    if type(check1[0]) != None:
TypeError: 'NoneType' object is not subscriptable

我想知道我能做些什么来避免这种情况？

谢谢。

Answer 1

在您的示例中，check1 将为None，因此您不能对其使用[0]。你可以这样做:

if check1 is not None:
    (error response)

或者只是使用 cur.rowcount 而不是 cur.fetchone():

if cur.rowcount > 0:
    (error response)