docs: def start_of_month(d, d_years=0, d_months=0):
      """
      Given a date, return a date first day of the month.
      
      @param d: The date to base the return value upon.
      @param d_years: Specify a delta in years to apply to date.
      @param d_months: Specify a delta in months to apply to date.
      
      @see http://code.activestate.com/recipes/476197-first-last-day-of-the-month/
      """
      y, m = d.year + d_years, d.month + d_months
      a, m = divmod(m-1, 12)
      return date(y+a, m+1, 1)