title: Python Pandas replace all values if index is larger than a date
body: <p>I am looking for some help on a pandas data frame.</p>
  
  <p>I have a data frame with the following structure</p>
  
  <pre><code>Date(indexed)      Total Clients   Sales Headcount    Total Products
  2019-11-01         1005            5                  4
  2019-12-01         1033            5                  5
  2020-01-01         1045            10                 6
  2020-02-01         1124            10                 10
  2020-03-01         1199            10                 11
  </code></pre>
  
  <p>How can I fill in the column total products with 0's if the date is after 2020-01-01?</p>
  
  <p>Expected outcome:</p>
  
  <pre><code>Date(indexed)      Total Clients   Sales Headcount    Total Products
  2019-11-01         1005            5                  4
  2019-12-01         1033            5                  5
  2020-01-01         1045            10                 6
  2020-02-01         1124            10                 0
  2020-03-01         1199            10                 0
  </code></pre>