title: How to empty out Listbox in PySimpleGUI
body: <p>I am brand new with PySimpleGUI but it's turning out to be really easy as advertised. After just a couple of hours I already have a halfway-working application.</p>
  <p>I'm using a Listbox to display several rows of items read in from a disk file. When I click my <em>Show Connections</em> button it reads the file and displays the items like I want. But if I click the button again, it reads the file again and now I have two copies in the box. I want to empty out the listbox before it gets updated from the next disk file read so that it always shows just exactly what is in the file. I have tried <em>Update</em> and <em>set_value</em> but can't seem to get anything to work.</p>
  <pre><code>layout_showdata = [
      [
      sg.Text('Time',size=(10,1)),
      sg.Text('Destination',size=(14,1)),
      sg.Text('Source',size=(14,1))],
      [sg.Listbox(size=(38,10),values=[''],key='_display_')]
  ]
  </code></pre>
  <p>.
  .
  .</p>
  <pre><code>    if event == 'Show Connections':
          print('Show Connections')
          window['panel_show'].update(visible=True)
          window['panel_edit'].update(visible=False)
          window['panel_entry'].update(visible=False)
          window['_display_'].set_value([])      ***#&lt;==This should do it I thought***
          with open('connections.txt','r') as cfile:
              schedule=csv.reader(cfile,dialect=&quot;pipes&quot;)
              for row in schedule:
                  items.append(row[0]+':'+row[1]+':'+row[2]+' '+row[3]+'   '+row[4])
                  print(items[itemnum])
                  itemnum+=1
              window.FindElement('_display_').Update(items)
  </code></pre>
  <p>I'm sure I'm missing something simple and would appreciate whatever help I can get.</p>
  <p>[EDIT] Added some running code to illustrate what happens. Instead of the listbox clearing when the button is pushed, it just reads the file again and adds to what is already there:</p>
  <pre><code>import PySimpleGUI as sg
  import csv
  items = []
  itemnum = 0
  csv.register_dialect('pipes', delimiter='|')
  
  file = [
  '01|23|45|12345678|87654321',
  '04|35|23|24680864|08642468',
  '01|23|45|12345678|87654321',
  '04|35|23|24680864|08642468',
  '01|23|45|12345678|87654321',
  '23|23|23|12341234|43214321'
  ]
  
  
  layout_showdata = [
          [
          sg.Text('Time',size=(10,1)),
          sg.Text('Destination',size=(14,1)),
          sg.Text('Source',size=(14,1))],
          [sg.Listbox(size=(38,10),values=[''],key='_display_')],
          [sg.Button('Show Connections')]
      ]
  window = sg.Window('XY Scheduler', layout_showdata)
  
  while True:
      event, values = window.Read(timeout=1)
      if event in (None, 'Quit'):
          break
  
  #Show Existing Connections
      
      if event == 'Show Connections':
          print('Show Connections')
          window['_display_'].update([])
          schedule=csv.reader(file,dialect=&quot;pipes&quot;)
          for row in schedule:
              items.append(row[0]+':'+row[1]+':'+row[2]+'         '+row[3]+'              '+row[4])
              print(items[itemnum])
              itemnum+=1
          window.FindElement('_display_').Update(items)
  </code></pre>