title: Check if a value exists in pandas dataframe
body: <p>I have a pandas dataframe which consists of 3000 latitude longitude values. I want to check if a lat-long exists in the dataframe or not.</p>
  
  <p>The data frame looks like the following:</p>
  
  <pre><code>lat      long
  31.76    77.84
  31.77    77.84
  31.78    77.84
  32.76    77.85
  </code></pre>
  
  <p>Now, I want to check if (31.76, 77.84) exists or not in the above dataframe. If yes, then the index also.</p>