title: timezone offset in datetime format in python 3.6
body: <p>This code is working on python 3.7 and failing on 3.6</p>
  
  <pre><code>from datetime import datetime
  try:
      d = datetime.strptime('2019-07-30T00:00:00.000-05:00', '%Y-%m-%dT%H:%M:%S.%f%z')
      print(d)
  
  except ValueError as ve:
      print(str(ve))
  </code></pre>
  
  <blockquote>
    <p>ValueError: time data '2019-07-30T00:00:00.000-05:00' does not match format '%Y-%m-%dT%H:%M:%S.%f%z'</p>
  </blockquote>
  
  <p>What's the format for timezone offset e.g. -05:00 in python 3.6?</p>