通过按钮调用函数时出现 Tkinter 错误

Question

So I'm trying to use some entry widgets in tkinter and then use a function that does multiple .get() commands at the same time. However I get an error that the function is not defined, even though they are within the same class. Here's the samples of the code:

def GetSubjects():
        subject1 = subject1entry.get()
        subject2 = subject2entry.get()
        subject3= subject3entry.get()

subjectConfirm.grid(row=3, column=0, command=GetSubjects)

As I said these are both in the same class and yet the button cannot call the function. I am relatively new to tkinter and this site so forgive me if this is easy stuff, but I just couldn't find a solution anywhere else.

Edit: Here's the whole class, I know my code is probably very suboptimal but this is my first large project I've tried

class Menu:

    def __init__(self, master):
        frame = tk.LabelFrame(master, text="Main Menu", padx=100, pady=10)
        frame.grid(row=0, column=0, padx=15, pady=15)
        # Create timetable button
        createTimetable = tk.Button(frame, text="Create Timetable", command=self.CreateTimetable)
        createTimetable.grid(row=0, column=0)
        # Exit program button
        exitProgram = tk.Button(frame, text="Exit Program", command=self.CloseWindow)
        exitProgram.grid(row=1, column=0)

    def CloseWindow(self):
        root.destroy()

    def GetSubjects():
        subject1 = subject1entry.get()
        subject2 = subject2entry.get()
        subject3 = subject3entry.get()

    def CreateTimetable(self):
        tableWindow = tk.Toplevel(root)
        tableWindow.title('Timetable Maker Window')
        tableWindow.geometry("800x500+400+200")
        # Subject labels
        subjectlabel1 = tk.Label(tableWindow, text="Enter your first subject:")
        subjectlabel2 = tk.Label(tableWindow, text="Enter your second subject:")
        subjectlabel3 = tk.Label(tableWindow, text="Enter your third subject:")
        # Subject entry boxes
        subject1entry = tk.Entry(tableWindow)
        subject2entry = tk.Entry(tableWindow)
        subject3entry = tk.Entry(tableWindow)
        # Puts subject entry boxes on screen
        subject1entry.grid(row=0, column=1)
        subject2entry.grid(row=1, column=1)
        subject3entry.grid(row=2, column=1)
        # Puts subject labels on screen
        subjectlabel1.grid(row=0, column=0)
        subjectlabel2.grid(row=1, column=0)
        subjectlabel3.grid(row=2, column=0)
        # Creates subject confirm button
        subjectConfirm = tk.Button(tableWindow,text="Press to confirm subjects")
        # Puts subject confirm button on screen
        subjectConfirm.grid(row=3, column=0, command=GetSubjects)
        print(subject1)
        print(subject2)
        print(subject3)

Answer 1

Your GetSubjects() method should look like this

def GetSubjects(self):
    subject1 = self.subject1entry.get()
    subject2 = self.subject2entry.get()
    subject3 = self.subject3entry.get()

Your CreateTimetable method should look like this (incomplete but give you the right idea)

def CreateTimetable(self):
    # Code removed for clarity
    self.subject1entry = tk.Entry(tableWindow)
    self.subject2entry = tk.Entry(tableWindow)
    self.subject3entry = tk.Entry(tableWindow)

And your callback for the button should look like this

subjectConfirm = tk.Button(tableWindow,text="Press to confirm subjects", command=self.GetSubjects)

The properties/methods need to be part of the Menu class so you use self. to tell python to make these properties of the current class (self is the typical convention but could be anything as long as you are consistent).

Oh and the print(subject1) parts need to be at the end of the GetSubjects method instead of where they currently are.