title: swapping two elements between two lists in python
body: <p>I'm trying to swap elements between two lists, and python doesn't seem to let that happen.</p>
  
  <pre><code>def swap(A,B,i,j):
      TEMP_B = B[j]
      B[j] = A[i]
      A[i] = TEMP_B
      return A,B
  
  X = np.array([[1.25,3],[1.5,2],[2,2.75],[2.25,2],[2,0.5],[3.25,0.75],
  [3.5,2.25],[4.25,0.75]])
  Y = np.array([[2.75,3.5],[3.25,3],[4.5,2.75],[3.5,4.75]])
  X,Y = swap(X,Y,1,1)
  OUTPUT:::
  Temp = [ 3.25  3.  ]
  before swap
  X[ 1 ]: [ 1.5  2. ]
  Y[ 1 ]: [ 3.25  3.  ]
  Temp = [ 1.5  2. ]
  after swap
  X[ 1 ]: [ 1.5  2. ]
  Y[ 1 ]: [ 1.5  2. ]
  </code></pre>
  
  <p>I expect B[j] = old A[i] and A[i] = old B[j]
  However, only one of the items gets swapped.. Not sure what the problem is.
  This is the output it get:</p>
  
  <p>I'm expecting X[1] = [3.25,3] but it comes out as [1.5,2]</p>