Sửa lỗi này thế nào ạ! (NameError: name 'fl' is not defined)

[Trancuong369 (Cuong)]

from tkinter import Frame, Tk, BOTH, Text, Menu, END
from tkinter.filedialog import Open

class Example(Frame):
    def __init__(self, parent):
        Frame.__init__(self, parent)
        self.parent = parent
        self.initUI()

    def initUI(self):
        self.parent.title("File dialog")
        self.pack(fill=BOTH, expand=1)

        menubar = Menu(self.parent)
        self.parent.config(menu=menubar)

        fileMenu = Menu(menubar)
        fileMenu.add_command(label="Open", command=self.onOpen)
        menubar.add_cascade(label="File", menu=fileMenu)

        self.txt = Text(self)
        self.txt.pack(fill=BOTH, expand=1)

    def onOpen(self):
        ftypes = [('Python files', '*.py'), ('All files', '*')]
        dlg = Open(self, filetypes = ftypes)
        fl = dlg.show()

    if fl != '':
        text = self.readFile(fl)
        self.txt.insert(END, text)
    
    def readFile(self, filename):
    f = open(filename, "r")
    text = f.read()
    return text

root = Tk()
ex = Example(root)
root.geometry("300x250+300+300")
root.mainloop()

[noname00 (HK boy)]

def onOpen(self):
     ftypes = [('Python files', '*.py'), ('All files', '*')]
     dlg = Open(self, filetypes = ftypes)
     fl = dlg.show()

 if fl != '':
     text = self.readFile(fl)
     self.txt.insert(END, text)

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