title: Convert string to timestamp python
body: <p>I'm trying to convert the list of str to the list of timestamps, then want to create the list of time delta of timestamps using total_seconds()</p>
  <pre><code>from datetime import datetime 
  a = ['091122333','092222222','093333333']
  for i in a:
      datetime.strptime(str(i),'%H:%M:%S.%f')
  print(a)
  </code></pre>
  <p>It shows the error code of time data '091122333' does not match format '%H:%M:%S.%f'</p>
  <p>I want to make timestamp 09(%H)11(%M)22(%S)333(%F) if possible.
  Could you give me the advice above?</p>
  <p>Thank you very much...</p>