名称错误：名称'；名称'；在tkinter中没有定义？

你好，我正在学习tkinter，当我运行这个程序时，我无法解决这个问题。 将tkinter作为tk导入 从tkinter进口* ''' master=tk.tk（）

当我运行它时，会出现以下错误： NameError:未定义名称“pocetnik”

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立即测试pocetnik和self。pocetnik是两种不同的东西。

class App():

def __init__(self, master):
    self.pocetnik_label = Label(master, text = 'Pocetnik')
    self.pocetnik_label.pack(side = LEFT)

    self.dodaj_button = Button(master, text = '+', command = pocetnik(self))
    self.dodaj_button.pack(side = RIGHT)

def pocetnik(self):
    master.widnows = tk.Toplevel(master)
    self.ime_label = Label(pocetnik, text = 'Ime').grid(row = 0, column = 0)
    self.ime_entry = Entry(pocetnik, bd = 5).grid(row = 0, column = 1)

pocetnik = App(master) 
master.mainloop()

from tkinter import *
from tkinter import ttk
import tkinter as tk
class App(ttk.Frame):

  def __init__(self, master):
      self.newwindow=master
      self.pocetnik_label = Label(master, text = 'Pocetnik')
      self.pocetnik_label.pack(side = LEFT)

      self.dodaj_button = Button(master, text = '+', command =self.pocetnik)
      self.dodaj_button.pack(side = RIGHT)
      self.newwindow.mainloop()

  def pocetnik(self):
      b2= tk.Toplevel(self.newwindow)
      self.ime_label = Label(b2, text = 'Ime').grid(row = 0, column = 0)
      self.ime_entry = Entry(b2, bd = 5).grid(row = 0, column = 1)

master=Tk()
pocetnik = App(master)