Python Tkinter GUI：“清除结果”按钮不起作用

Question

This is my first python program. I'm trying to create torricelli's draintime calculator, but the 'clear result' button doesn't work. I want it to clear calculated results.

I get this error:

Traceback (most recent call last):
    File "C:\Users\David \Desktop  File\GUI_DrainTime_Calculator.py", line 83, in clear
    drain_label.destroy()
NameError: name 'drain_label' is not defined

Please help me figure why this NameError persists. this is the culprit:

drain_label = Label(
    WIN, 
    font=('Helvetica', 8, 'bold'),
    text="The time it takes for the liquid to drain is: %.0f hour, %.0f minutes, and %.0f seconds." % (hr, Min, sec)).pack(side=BOTTOM)

def clear():
    drain_label.destroy()
    Clearbtn = Button(WIN, text="Clear Results", font('Helvetica',7,'bold'), fg='black',command=clear)
    Clearbtn.configure(background='grey')
    Clearbtn.pack(side=TOP,pady=5)

Thank you all !

Answer 1

Try using a textvariable for your label. I also recommend using a Class for your program.

import tkinter as tk
from tkinter import ttk

class Calculator:
    def __init__(self, master):

        frame = tk.Frame(master)

        self.text_var = tk.StringVar()
        hr, min, sec = 1, 4, 20
        text = 'drain time = %.0f Hr, %0f Min, %.0f Sec' % (hr, min, sec)

        drain_label = ttk.Label(frame, textvariable=self.text_var).pack()

        clear_button = ttk.Button(frame, text='clear', command=self.destroy).pack()

        frame.pack()

    def destroy(self):
        self.text_var.set('')

root = tk.Tk()
app = Calculator(root)
root.mainloop()

you can use tk.StringVar() along with the .get() and .set() methods to get and set the string variable. you could also use string variables for hr, min, sec and pass those using a button.

Answer 2

您的变量drain_label不是global的，因此该功能无法看到它的定义/声明的任何地方，尝试通过drain_label作为参数在函数或使其global ，虽然使用全局变量，尽可能我建议回避。