TypeError:'NoneType'对象不可订阅

Question

错误: names = curfetchone()[0]

TypeError: 'NoneType' object is not subscriptable. 

我试过检查缩进但仍然有错误.我读到如果数据库中没有文件名记录,那么变量名称可能会返回'None'.

我在其他'def'中使用相同的变量'names',它工作正常.我确定它与返回的'None'值有关.

global filename
global t
try:
    con = sqlite3.connect('textdb.db')
    cur = con.cursor()

    filename = tkinter.simpledialog.askstring("Open file...", "Input filename to open:")

    if filename != None:
        cur.execute("SELECT file_name FROM file_info WHERE file_name = ?", (filename,))
        names = cur.fetchone()[0]
        same = str(names)
        if filename == same:
            cur.execute("SELECT file_content FROM file_info WHERE file_name = ?", (filename,))
            content = cur.fetchone()[0]
            t = str(content)
            text.delete(0.0, END)
            text.insert(0.0, t)
        else:
            result = tkinter.messagebox.askyesno(title="File doesn't exist", message="'"+(filename)+"' doesn't exist. Make a new file using '"+(filename)+"'?")
            if result == True:
                cur.execute("SELECT COUNT(*) FROM file_info")
                count_row = cur.fetchone()
                cntdata = count_row[0]
                incr = (cntdata + 1)
                t = str(text.get(0.0, END))
                curtime = str(ctime())
                cur.execute("INSERT OR IGNORE INTO file_info VALUES(?, ?, ?, ?, ?)", (incr, filename, t, curtime, curtime,))
                con.commit()

except sqlite3.Error:
    if con:
        con.rollback()
finally:
    if con:
        con.close()

Answer 1

如果由于某种原因(空结果集？)curfetchone()返回None,[0]则当然禁止访问(如错误消息所示).

所以最好分两步完成

row = curfetchone()
if row is not None: 
    names = row[0]
    # proceed
else:
    # act appropriately