title: List updating itself after variable appending in it changes
body: <pre><code>mainData = []
  data = []
  newEntry = [1,2,3]
  data.append(newEntry)
  mainData.append(data)
  print(mainData)
  anotherEntry = [4,5,6]
  data.append(anotherEntry)
  thirdEntry = [7,8,9]
  data.append(thirdEntry)
  print(mainData)
  
  OP =&gt;
  [[[1, 2, 3]]]
  [[[1, 2, 3], [4, 5, 6], [7, 8, 9]]]
  </code></pre>
  <p>Why my 'mainData' is changing when i'm only appending data in 'data' variable?</p>