title: Adding items from one tkinter listbox to another
body: <p>I have two tkinter listboxes (parent and child) and two buttons (add_button and remove_button).
  The child listbox gets items from the parent listbox via the add_button and there is an option of removing the items from
  the child listbox via the remove_button.</p>
  
  <p>My problem is that after the GUI is loaded and the add_button is pressed, the first item in the parent listbox is
  added to the child listbox even if it is not ACTIVE. The same happens to the child_frame, in that the first item is removed
  after pressing the remove_button even if it is not ACTIVE. I want a way to prevent this. Additionally, I want an item to
  be added to the child listbox only once no matter how many times the add_button is pressed.</p>
  
  <p>The code below is a part of another bigger code. Any help will be valued in solving the problems outlined above.
  Thanks in advance.</p>
  
  <p>Here is the code:</p>
  
  <pre><code>from Tkinter import *
  
  root = Tk()
  root.geometry('330x200')
  
  names = ['Bill', 'Jack', 'Joanne', 'Ann', 'Dave', 'Jane']
  
  
  def add_name():
      x = parent.get(ACTIVE)
      child.insert(END, x)
  
  
  def remove_name():
      child.delete(ACTIVE)
  
  
  parent = Listbox(root)
  for name in names:
      parent.insert(END, name)
  
  parent.place(x=5, y=5)
  
  add_button = Button(root, text='Add',
                      command=add_name)
  add_button.place(x=148, y=5)
  
  remove_button = Button(root, text='Remove',
                         command=remove_name)
  remove_button.place(x=138, y=50)
  
  child = Listbox(root)
  child.place(x=200, y=5)
  
  root.mainloop()
  </code></pre>