title: adding,subtracting datetime.time columns pandas
body: <p>I have following dataframe</p>
  
  <pre><code>flight_departure   arrival_at_desination   boarding  total_flight_time   total_flight_time/2    time_to_collect_bags
  0:00                     4:00               23:30           4:00                  2:00                     4:30
  9:00                     14:30              8:30            5:30                  2:45                      15:00
  
  flight_departure- 0:00 signifies 12:00 AM
  arrival_at_desination- 4:00 signifies 4 AM
  boarding = flight_departure-30 minutes(23:30)
  total_flight_time=arrival_at_desination-flight_departure(4 hours)
  
  total_flight_time/2-calculates hald time(2 hours in this case)
  time_to_collect_bags=arrival_at_desination+30 minutes(4:30AM)
  </code></pre>
  
  <p>When I try to do the following</p>
  
  <pre><code>df['arrival_at_desination']-df['flight_departure']
  </code></pre>
  
  <p>It gives me following error</p>
  
  <pre><code>TypeError: unsupported operand type(s) for -: 'datetime.time' and 'datetime.time'
  </code></pre>
  
  <p>how should I subtract two datetime.time columns?</p>