title: Why do I get a type error when I attempt to update the value attribute of Progressbar in Tkinter?
body: <p>I am using Python 3.8.2
  I have the following code that has 3 main loops. I need a simple UI that shows the progress for each loop.</p>
  
  <pre><code>import tkinter as tk
  from tkinter import filedialog, ttk
  from tkinter.ttk import Progressbar
  import json
  class App(tk.Tk):
  
      def __init__(self):
          tk.Tk.__init__(self)
          self.filename = ''
          tk.Button(self, text = 'Upload File', command = self.get_file).grid(row = 0, column = 0)
          tk.Button(self, text = 'Verify', command = self.verify).grid(row = 1, column = 0)
          # tk.Label(self, text = 'some name').grid(row = 0, column = 1)
          self.mainloop()
  
      def get_file(self):
          self.filename = tk.filedialog.askopenfilename(title = "Select File", filetypes = [("JSON", "*.json")])
          tk.Label(self, text = self.filename).grid(row = 0, column = 1)
      def verify(self):
          tk.Label(self, text = 'Verifying Trustee Public Keys').grid(row = 2, column = 0)
          ttk.Progressbar(self,
                     length = 100,
                     orient = "horizontal",
                     maximum = len(self.data["trustee_public_keys"]),
                     value = 0).grid(row = 3, column = 0)
          i = 1
          for trustee_key_list in self.data['trustee_public_keys']:
              print('Trustee :', i)
              //some code
              i = i+1
              ttk.Progressbar['value'] =  i
  </code></pre>
  
  <p>Everytime I run it I get the error:</p>
  
  <pre><code> File "C:/Users/Student User/AppData/Roaming/JetBrains/PyCharmCE2020.1/scratches/scratch_17.py", line 81, in verify
  ttk.Progressbar['value'] =  i
  TypeError: 'type' object does not support item assignment
  </code></pre>
  
  <p>What am I doing wrong and how do I get the intended result?</p>