title: Update Tkinter progress bar
body: <p>I've made a python script for downloading a number of files from a website and I'd like to make a progress bar in Tkinter which should update as each file is saved to the computer. I've seen some examples using OOP but I'm still getting to grips with OOP and one day hope to understand why people use OOP when making GUI apps in Tkinter. Perhaps a kind user could clarify this for me.</p>
  
  <p>My code is shown here:</p>
  
  <pre><code>from Tkinter import *
  import ttk
  import numpy as np
  
  global files
  files = np.arange(1,1000000)
  
  def loading():
      global downloaded
      downloaded = 0
      for i in array:
          downloaded +=1
  
  root = Tk()
  
  progress= ttk.Progressbar(root, orient = 'horizontal', maximum = 1000000, value = downloaded, mode = 'determinate')
  progress.pack(fill=BOTH)
  start = ttk.Button(root,text='start',command=loading)
  start.pack(fill=BOTH)
  
  root.mainloop()
  </code></pre>
  
  <p>I've made a variable which represents the number of files (I'm not really trying to download 1000000 files, this was just some code to get the progress bar working).</p>
  
  <p>The code should run the loading function when the start button is clicked but it doesn't. I'd greatly appreciate any help you can give me on this issue =)</p>