title: Make a list out of two (or more) lists which refers to the original lists when appending new element
body: <p>I would like to create a list of objects which stands for the whole category of objects with the same attribute (let's say the objects that are visible). But once I append the object to one of the subgroups it doesn't update the list of all visible objects (visible_objects). This is known Python behaviour to me but I would like to know what is the best practice to implement this so it appends the element also to the combined list (visible_objects) in a clean and seamless way. (i.e. everytime I append new element to one of the subgroups)</p>
  <pre><code>class A:
      def __init__(self,i):
          self.i=i
             
  images=[A(1),A(2),A(3)]
  images2=[A(4),A(5)]
  
  visible_objects=images+images2
  
  images.append(A(6))
  
  print([x.i for x in images])
  print([x.i for x in images2])
  print([x.i for x in visible_objects])
  
  [1, 2, 3, 6]
  [4, 5]
  [1, 2, 3, 4, 5]
  </code></pre>
  <p>I want the last list also contain 6 without reassigning visible_objects after every append. Thank you very much.</p>