title: Existing list overwritten when creating a new list
body: <p>In the script below, something strange happens when the second loop starts. The list <code>area_1</code> changes value even though it is not involved in that loop at all. Same happens with <code>area_2</code> after the third loop.</p>
  <pre><code>server_1 = 'x1'
  server_2 = 'x2'
  server_3 = 'x3'
  table = [
      {'Terminal': 'site_1', 'City': 'London', 'Station': server_1},
      {'Terminal': 'site_2', 'City': 'London', 'Station': server_1},
      {'Terminal': 'site_3', 'City': 'London', 'Station': server_2},
      {'Terminal': 'site_4', 'City': 'New York', 'Station': server_3},
      {'Terminal': 'site_5', 'City': 'New York', 'Station': server_1},
      {'Terminal': 'site_6', 'City': 'New York','Station': server_2},
      {'Terminal': 'site_7', 'City': 'Tokyo', 'Station': server_3},
      {'Terminal': 'site_8', 'City': 'Tokyo', 'Station': server_3},
      {'Terminal': 'site_9', 'City': 'Tokyo', 'Station': server_2}    
  ]
  city_index = [ 
      {'City':'London', 'Lat': 51.48,'Long': -0.14 },
      {'City':'New York', 'Lat': 40.69,'Long': -74.26 },
      {'City':'Tokyo', 'Lat': 35.51,'Long': 138.64 }
  ]
  area_1 = []
  for i in city_index:
      area_1.append(i)
      area_1[-1].update({'Station': server_1, 'Count of terminals': sum(q['City'] == i['City'] and q['Station'] == server_1 for q in table)})
  area_2 = []
  for i in city_index:
      area_2.append(i)
      area_2[-1].update({'Station': server_2, 'Count of terminals': sum(q['City'] == i['City'] and q['Station'] == server_2 for q in table)})
  area_3 = []
  for i in city_index:
      area_3.append(i)
      area_3[-1].update({'Station': server_3, 'Count of terminals': sum(q['City'] == i['City'] and q['Station'] == server_3 for q in table)})
  
  all = area_1 + area_2 + area_3
  
  for i in all:
      print(i)
  </code></pre>
  <p>Output: (Notice the station key)</p>
  <pre><code>{'City': 'London', 'Lat': 51.48, 'Long': -0.14, 'Station': 'x3', 'Count of terminals': 0}
  {'City': 'New York', 'Lat': 40.69, 'Long': -74.26, 'Station': 'x3', 'Count of terminals': 1}
  {'City': 'Tokyo', 'Lat': 35.51, 'Long': 138.64, 'Station': 'x3', 'Count of terminals': 2}
  {'City': 'London', 'Lat': 51.48, 'Long': -0.14, 'Station': 'x3', 'Count of terminals': 0}
  {'City': 'New York', 'Lat': 40.69, 'Long': -74.26, 'Station': 'x3', 'Count of terminals': 1}
  {'City': 'Tokyo', 'Lat': 35.51, 'Long': 138.64, 'Station': 'x3', 'Count of terminals': 2}
  {'City': 'London', 'Lat': 51.48, 'Long': -0.14, 'Station': 'x3', 'Count of terminals': 0}
  {'City': 'New York', 'Lat': 40.69, 'Long': -74.26, 'Station': 'x3', 'Count of terminals': 1}
  {'City': 'Tokyo', 'Lat': 35.51, 'Long': 138.64, 'Station': 'x3', 'Count of terminals': 2}
  </code></pre>
  <p>All 3 lists become identical at the end = <code>area_3</code>.
  Can someone please explain why this is happening? Why are <code>area_1</code> and <code>area_2</code> being overwritten?</p>