title: Assign same random value to A-B , B-A pairs in python Dataframe
body: <p>I have a Dataframe like</p>
  
  <pre><code> Sou  Des
    1    3
    1    4
    2    3
    2    4
    3    1
    3    2
    4    1
    4    2
  </code></pre>
  
  <p>I need to assign random value for each pair between 0 and 1 but have to assign the same random value for both similar pairs like "1-3", "3-1" and other pairs. I'm expecting a result dataframe like</p>
  
  <pre><code> Sou  Des   Val
    1    3    0.1
    1    4    0.6
    2    3    0.9
    2    4    0.5
    3    1    0.1
    3    2    0.9
    4    1    0.6
    4    2    0.5
  </code></pre>
  
  <p>How to assign same random value similar pairs like "A-B" and "B-A" in python pandas .</p>