from datetime import datetime


def reformat_subway_dates(date):
    """
    The dates in our subway data are formatted in the format month-day-year.
    The dates in our weather underground data are formatted year-month-day.

    In order to join these two data sets together, we'll want the dates formatted
    the same way.  Write a function that takes as its input a date in the MTA Subway
    data format, and returns a date in the weather underground format.

    Hint: 
    There are a couple of useful functions in the datetime library that will
    help on this assignment, called strptime and strftime. 
    More info can be seen here and further in the documentation section:
    http://docs.python.org/2/library/datetime.html#datetime.datetime.strptime
    """
    struct_time = datetime.strptime(date, "%m-%d-%y")
    date_formatted = datetime.strftime(struct_time, "%Y-%m-%d")

    return date_formatted