Reformat Date — Python

# Time:  O(n)
# Space: O(1)

class Solution(object):
    def reformatDate(self, date):
        """
        :type date: str
        :rtype: str
        """
        lookup = {"Jan":1, "Feb":2, "Mar":3, "Apr":4,
                  "May":5, "Jun":6, "Jul":7, "Aug":8,
                  "Sep":9, "Oct":10, "Nov":11, "Dec":12}
        return "{:04d}-{:02d}-{:02d}".format(int(date[-4:]), lookup[date[-8:-5]], int(date[:date.index(' ')-2]))