在Tkinter的儿童中打包和网格

Question

I understand you can not mix tkinter's grid() and pack() methods within the same master. However, my understanding was that it is valid to use pack within a frame, and grid within a different frame, even if both of these frames share a common parent? Here is my code for a frame that is packed onto the master root, Why am I receiving the error regarding mixing pack and grid? Sorry if this is just me blindly missing the rules of mixing pack and grid.

Class Login(tk.Frame): 
    def __init__(self, master):
        super().__init__(master)
        self.config()

        rightFrame = tk.Frame(self).pack(side='right') #Using PACK
        leftFrame = tk.Frame(self).pack(side='left') #Using GRID

        # RIGHT SIDE #

        self.photo = tk.PhotoImage(file='temp.png')
        label = tk.Label(rightFrame, image=self.photo)
        label.pack(side='right')

        # LEFT SIDE #

        label = tk.Label(leftFrame, text="Grade Predictor")
        label.config(font=("Courier 22 bold"))
        label.grid(row=0, column=0)

        self.usernameBox = tk.Entry(leftFrame)
        self.usernameBox.grid(row=1, column=0)       

        self.pack(fill='both')

Answer 1

You are creating the left and right frames as:

rightFrame = tk.Frame(self).pack(side='right')

which assigns None to rightFrame as pack() returns None .

If you create them as:

rightFrame = tk.Frame(self)
rightFrame.pack(side='right')

it works just fine.