Question

我的逻辑/ if / else语句似乎有问题！问题在于，如果我输入错误的密码，但可以说正确的用户名，没有任何反应，类似的情况发生在学生和老师身上，我只是不确定要改变什么。谢谢。

错误：

 File "/Users/Sebastian/Desktop/DQS/login.py", line 43, in _login_btn_clickked
    if ( student_usernames.index(username) == student_passwords.index(password) ):
ValueError: tuple.index(x): x not in tuple



from tkinter import *
import tkinter.messagebox as tm


class LoginFrame(Frame):
    def __init__(self, master):
        super().__init__(master)

        self.label_1 = Label(self, text="Username")
        self.label_2 = Label(self, text="Password")

        self.entry_1 = Entry(self)
        self.entry_2 = Entry(self, show="*")

        self.label_1.grid(row=0, sticky=E)
        self.label_2.grid(row=1, sticky=E)
        self.entry_1.grid(row=0, column=1)
        self.entry_2.grid(row=1, column=1)

        self.checkbox = Checkbutton(self, text="Keep me logged in")
        self.checkbox.grid(columnspan=2)

        self.logbtn = Button(self, text="Login", command = self._login_btn_clickked)
        self.logbtn.grid(columnspan=2)

        self.pack()

    def _login_btn_clickked(self):
        #print("Clicked")
        username = self.entry_1.get()
        password = self.entry_2.get()

        #print(username, password)

        student_usernames = ("C100", "C200", "C300")
        student_passwords = ("PASS", "PASS1", "PASS2")

        teacher_usernames = ("T100", "T200", "T300")
        teacher_passwords = ("TPASS", "TPASS1", "TPASS3")


        if username in student_usernames:
            if ( student_usernames.index(username) == student_passwords.index(password) ):
                tm.showinfo("Login info", "Welcome Student")
            else:
                tm.showerror("Login error", "Incorrect information")
        elif username in teacher_usernames:
            if ( teacher_usernames.index(username) == teacher_passwords.index(password) ):
                tm.showinfo("Login info", "Welcome Teacher")
            else:
                tm.showerror("Login error", "Incorrect information")
        else: 
            tm.showerror("Login error", "Incorrect information")



root = Tk()
lf = LoginFrame(root)
root.mainloop()

Answer 1

您假设输入密码始终位于您定义为包含密码的元组之一中。你可以很容易地打破这个，简单地传入一个未包含在其中一个元组中的东西。你是条件中断，因为你在错误信息中看到它试图找到该值的索引，但它甚至不在元组中。因此，ValueError例外。

您需要检查密码是否在相应的学生/教师密码元组以及用户名中，然后您可以检查索引。

所以，这将是if username in student_usernames and password in student_passwords:作为一个例子。

或者，您可以通过DeMorgan的法律扭转逻辑并使用：

if not (username in student_usernames or password in student_passwords)

Answer 2

student_passwords.index(password)假设password实际存在student_passwords。您可以改为使用if username in student_usernames and password in student_passwords:或使用try: except ValueError:

包围整个块

E.g。

if username in student_usernames and password in student_passwords:
    if ( student_usernames.index(username) == student_passwords.index(password) ):
        tm.showinfo("Login info", "Welcome Student")
    else:
        tm.showerror("Login error", "Incorrect information")
elif username in teacher_usernames and password in teacher_passwords:
    if ( teacher_usernames.index(username) == teacher_passwords.index(password) ):
        tm.showinfo("Login info", "Welcome Teacher")
    else:
        tm.showerror("Login error", "Incorrect information")
else: 
    tm.showerror("Login error", "Incorrect information")

else语句问题，tkinter，python

2 个答案: