title: Creating a new dataframe column by comparing strings of two unequal dataframes
body: <p>What is the most efficient approach in Python to create a new data frame column <code>df1['Description']</code> obtained when <code>df1['a']</code> string is equal <code>df2['b']</code> string? When condition is met, then a separate string <code>df2['Description']</code> would be assigned to <code>df1['Description']</code>. <code>df1</code> and <code>df2</code> are large data frames (~1/2 Million rows) of unequal sizes.</p>
  <p><code>df1</code>:</p>
  <pre><code>a    b
  Z0   1  
  Z1   2
  A7   3
  </code></pre>
  <p><code>df2</code>:</p>
  <pre><code>b    Description
  W2   asadsde  
  Z0   evrverve
  A7   eveveerv
  </code></pre>
  <p>I would like:</p>
  <pre><code>df1
  a    b   Description
  Z0   1   evrverve  
  Z1   2   jsbdbcje
  A7   3   eveveerv
  </code></pre>