title: What is the quickest way to increment date string YYYY-MM-DD in Python?
body: <p>In Pandas, I am using dates with string format <code>YYYY-MM-DD</code> 
  What is the quickest way to increment the date with the result in <code>YYYY-MM-DD</code> format?</p>
  
  <pre><code>d1 = '2018-02-10'
  </code></pre>
  
  <p>I want to increment it by 1 and get the result back as a string:</p>
  
  <pre><code>d1_inc = '2018-02-11'
  </code></pre>