title: Making a line in a matrix go up (Python) - issue with Append that replace instead of Appending item
body: <p>I want to make an "animation" of an element of matrix going from the bottom line to the top ligne of the matrix.
  I have the following code, but something not wanted is ongoing with append function : </p>
  
  <pre><code>import time
  #size of the matrix
  PixelCarac=4
  #List that cointain all the matrixs
  ListMatrix=[]
  #matrix  filled with 0
  tempo =[[0 for x in range(PixelCarac)] for y in range(PixelCarac)] 
  #last line have a difference
  tempo[3][0]=1
  print("First step")
  print(tempo)    
  
  #making the line going up.  
  for x in range(0,PixelCarac-1,1):   
      #append in the list
      ListMatrix.append(tempo)
      #display 
      print("length of the list is " + str(len(ListMatrix)))
      for elem in ListMatrix:
          print(elem)     
  
      #Making the line going up by recopie from 1 line to the upper one
      for i in range(0,len(tempo)-1,1):   
          tempo[i]=tempo[i+1]                     
  
  time.sleep(20)
  </code></pre>
  
  <p><strong>the ouput I have is :</strong></p>
  
  <p>First step</p>
  
  <p>[[0,0,0,0],[0,0,0,0],[0,0,0,0],[0,0,0,1]</p>
  
  <p>length of the list is 1</p>
  
  <p>[[0,0,0,0],[0,0,0,0],[0,0,0,0],[0,0,0,1]</p>
  
  <p>length of the list is 2</p>
  
  <p>[[0,0,0,0],[0,0,0,0],[0,0,0,<strong>1</strong>],[0,0,0,1]</p>
  
  <p>[[0,0,0,0],[0,0,0,0],[0,0,0,1],[0,0,0,1]</p>
  
  <p>length of the list is 2</p>
  
  <p>[[0,0,0,0],[0,0,0,<strong>1</strong>],[0,0,0,<strong>1</strong>],[0,0,0,1]</p>
  
  <p>[[0,0,0,0],[0,0,0,<strong>1</strong>],[0,0,0,1],[0,0,0,1]</p>
  
  <p>[[0,0,0,0],[0,0,0,1],[0,0,0,1],[0,0,0,1]</p>
  
  <p><strong>the ouput I want is  :</strong></p>
  
  <p>First step</p>
  
  <p>[[0,0,0,0],[0,0,0,0],[0,0,0,0],[0,0,0,1]</p>
  
  <p>length of the list is 1</p>
  
  <p>[[0,0,0,0],[0,0,0,0],[0,0,0,0],[0,0,0,1]</p>
  
  <p>length of the list is 2</p>
  
  <p>[[0,0,0,0],[0,0,0,0],[0,0,0,0],[<strong>0</strong>,0,0,1]</p>
  
  <p>[[0,0,0,0],[0,0,0,0],[0,0,0,1],[0,0,0,1]</p>
  
  <p>length of the list is 2</p>
  
  <p>[[0,0,0,0],[0,0,0,<strong>0</strong>],[0,0,0,<strong>0</strong>],[0,0,0,1]</p>
  
  <p>[[0,0,0,0],[0,0,0,<strong>0</strong>],[0,0,0,1],[0,0,0,1]</p>
  
  <p>[[0,0,0,0],[0,0,0,1],[0,0,0,1],[0,0,0,1]</p>
  
  <p><strong>Question :</strong> </p>
  
  <p>Why the <em>append</em> function is changing the previous items in the list?</p>