Python 3.x Python ttk标签错误，标签未定义

我已经为一个闹钟编写了以下代码，在GitHub上找到了它。但是在我的代码中，它抛出了一个错误，表示标签没有定义

import time as time, os as os
from tkinter import *
from tkinter import messagebox
from tkinter import ttk  # For buttons, labels, frames etc...

root = Tk()  # Creates the tkinter object root
root.title('Alarm Clock')  # Sets the window title
root.geometry('200x200')  # Sets the window dimension


def submit_button():  # The core condition for the alarm clock
     alarm_time = time_entry.get()
     dialog_box()
     #bottom_label.config(text ="The Alarm will Ring at {} ".format(AlarmTime))  #delayed in execution
     current_time = time.strftime('%H:%M')  # Sets the current_time format to Hours:Minutes
     print('The alarm time is: {}' .format(alarm_time))
     while alarm_time != current_time:
         current_time = time.strftime('%H:%M')  # Sets the current_time format to Hours:Minutes
         time.sleep(1)  # To give a delay in while loop 
     if alarm_time == current_time:  # When current_time is alarm time
         os.system('start alarm-music.mp3')  # Play the music from the os
         bottom_label.config(text="Alarm music playing....")
         messagebox.showinfo(title='Alarm Message', message="{}".format(entry2.get()))


def dialog_box():
    alarm_time = time_entry.get()
    messagebox.showinfo("Alarm Clock", "alarm will ring at {}" .format(alarm_time))  # title and display of dialog box.
    bottom_label.config(text = "The alarm time is counting...")  # configures the text below submit button


# Frame creation
alarm_frame = ttk.Frame(root)  # Creates a frame named alarm_frame
alarm_frame.config(height=200, width=200)  # Sets the dimensions of the frame
alarm_frame.pack()

# Alarm Label
alarm_label = ttk.Label(alarm_frame, text = "Enter the alarm time:")  # Creates a label with text Enter alarm time
alarm_label.pack()  # Unpacks the label onto the frame

# Entering time
time_entry = ttk.Entry(alarm_frame, width=30)  
time_entry.insert(3, 'example: 13:15')  
time_entry.pack()  # Unpacks the entry on the frame

 # Message label
message_label = ttk.Label(alarm_frame, text = "Enter message to display:")
message_label.pack()

# Entering Message
message_entry = ttk.Entry(alarm_frame, width = 30)  # Facilitates entering    alarm message
message_entry.pack()  # Unpacks the entry area

# Creation of submit button
submit = ttk.Button(alarm_frame, text = 'submit', command = submit_button())     
submit.pack()  # Unpacks the button onto the frame


# Bottom label creation
bottom_label = ttk.Label(alarm_frame)  # Label(master, **kw)
bottom_label.pack()  # unpacks the bottom_label on the frame

root.mainloop()  

它表示在对话框（）中未定义底部标签。为什么会发生这种情况？

使用：

...
# Bottom label creation
bottom_label = ttk.Label(alarm_frame)  # Label(master, **kw)
bottom_label.pack()  # unpacks the bottom_label on the frame

# Creation of submit button
submit = ttk.Button(alarm_frame, text = 'submit', command = submit_button())     
submit.pack()  # Unpacks the button onto the frame
...

而不是：

...
# Creation of submit button
submit = ttk.Button(alarm_frame, text = 'submit', command = submit_button())     
submit.pack()  # Unpacks the button onto the frame


# Bottom label creation
bottom_label = ttk.Label(alarm_frame)  # Label(master, **kw)
bottom_label.pack()  # unpacks the bottom_label on the frame
...

---

订单事宜，在

命令=

中使用它之前，您必须初始化

bottom\u标签

对不起，我不能很清楚地理解它，请您再解释一下好吗？我希望现在已经清楚了。另外，您可能希望摆脱

while

循环。我发现错误出现在按钮处理程序回调中，我在回调中使用了一个不必要的paratenthesis，in命令。在我删除它之后，程序按预期工作