tkinter Button callback function not being called

You have a few things wrong with your code:

1. onClick needs the "self" param passed to it and you need to update "command=onClick" to "command=self.onClick"

2. Your entry1 variable should be set to an instance variable by prepending it with "self" so that it is accessible from the onClick method. Variable scope is a little different in python OOP.

from tkinter import *from tkinter import messageboxfrom tkinter import ttkfrom tkcalendar import DateEntryclass Memo(Frame):    def __init__(self,master):        Frame.__init__(self,master)        self.master=master        self.master.title('Memo')        self.pack(fill=BOTH, expand=True)        frame1=Frame(self,width=500,height=50)        frame1.pack(expand=False)        label1=Label(frame1,text='Amount',width=10)        label1.pack(side=LEFT, padx=10,pady=10)        self.entry1=Entry(frame1,width=20)        self.entry1.pack(padx=10,fill=X,expand=True)        frame2=Frame(self,width=500,height=50)        frame2.pack(expand=False)        label2=Label(frame2,text='Cartegory',width=10)        label2.pack(side=LEFT, padx=10,pady=10)        listbox1=Listbox(frame2,width=20)        listbox1.insert(END,"식료품비","잡화비","건강관리비","외식비")        listbox1.pack(side=LEFT, padx=10,pady=10)        frame3=Frame(self,width=500,height=50)        frame3.pack(expand=False)        label3=Label(frame3,text='Date',width=10)        label3.pack(side=LEFT, padx=10,pady=10)        dateentry = DateEntry(frame3)        dateentry.pack(padx=10,pady=10)        frame4=Frame(self,width=500,height=500)        frame4.pack(expand=False)        button1=Button(frame4,text='csv Export',command=self.okClick)        button1.pack(side=LEFT,padx=10,pady=10)    def okClick(self):        name = self.entry1.get()        messagebox.showinfo("이름", name)if __name__ == "__main__":    a=Memo(Tk())    a.mainloop()