title: How to alter the time in python?
body: <p>I wanted to change the minutes/hours of pythonic time.
  I have a string of time <code>start_time = "2013-09-30 14:12:08.024923"</code>. I want it to convert it to its ceil quater,half or full time, ie if I set interval as <code>15</code> I should get <code>2013-09-30 14:15:00.0000</code>. If interval is <code>30</code>, I should get <code>2013-09-30 14:15:00.0000</code></p>
  
  <p>How can I change it?</p>
  
  <p>Here is what I have tried.</p>
  
  <pre><code>start_time = "2013-09-30 14:12:08.024923"
  start_time  = datetime.datetime.strptime(start_time, "%Y-%m-%d %H:%M:%S.%f")
  interval = 15
  ceil_to = (start_time.minute/interval) *interval + interval
  
  start_time.minute = interval # throws error saying attribute 'minute' of 'datetime.datetime' objects is not writable
  </code></pre>
  
  <p>How do I achieve this?</p>