import pytz
from datetime import datetime


def date_string_to_object_utc(date_string):
  """Converts a RFC3339 date string to a datetime object as UTC.

  Args:
    date_string: RFC 3339 date string (e.g: 2017-12-27T00:00:00Z).

  Returns:
    Corresponding datetime object with timezone set to UTC.
  """
  return pytz.utc.localize(datetime.strptime(date_string, '%Y-%m-%dT%H:%M:%SZ'))