import calendar
import datetime

def subtract_years(date, years):
    """Subtract a number of years from a given date.

    >>> d = datetime.date(year=2012, month=2, day=29)
    >>> subtract_years(d, 1)
    datetime.date(2011, 2, 28)
    >>> subtract_years(d, 4)
    datetime.date(2008, 2, 29)
    """

    year = date.year - years
    month = date.month
    day = date.day
    
    if month == 2 and day > 28:
        if not calendar.isleap(year):
            day = 28
    
    return datetime.date(year=year, month=month, day=day)