title: Python Pandas : Create new rows from values of a List Column
body: <p>I have a Pandas Dataframe that look like this : </p>
  
  <pre><code>              tags   value
  [tag1, tag2, tag3]       0
  [tag2, tag3]            10
  [tag1, tag3]            50
                         ...
  </code></pre>
  
  <p>On this Dataframe, I want to apply a function that, for each tags of each rows, will create a new row with a column 'tag', and a column 'related_tags'. 
  Here is an example of what I am expecting : </p>
  
  <pre><code> tag   value    related_tags
  tag1       0    [tag2, tag3] 
  tag2       0    [tag1, tag3] 
  tag3       0    [tag1, tag2] 
  tag2      10    [tag3]     
  tag3      10    [tag2]    
  tag1      50    [tag3]   
  tag3      50    [tag1]
  </code></pre>
  
  <p>I am familiar with Spark DataFrames but not with Pandas, is there a simple way to achieve this ?</p>