code: def get_us_dst_start(year):
      """For each year, it returns the second Sunday in March,
      which is the start of the daylight saving (DST) in US/Canada.
  
      We assume DST starts on Second Sunday of March at 2 a.m.
  
      Parameters
      ----------
      year : `int`
          Year for which DST start date is desired.
  
      Returns
      -------
      result : `datetime.datetime`
          The timestamp of start of DST in US/Canada.
      """
      # Finds a date in third week of March.
      date_in_3rd_week = datetime(year, 3, 15, 2)
      # Finds out which week day it is:
      weekday = date_in_3rd_week.weekday()
      # Finds the Sunday before that by going back to Monday and does an extra -1.
      second_sunday_date = date_in_3rd_week.replace(
          day=(15 - weekday - 1)
      )
      return second_sunday_date
  
imports: import math
  from datetime import datetime
  from datetime import timedelta
  import numpy
  import pandas
  import pytz
  from holidays_ext import get_holidays
  from pandas.tseries.frequencies import to_offset
  from scipy.special import expit
  from greykite.common import constants
  from greykite.common.python_utils import split_offset_str
label_desc: Use image node_id 4 for calling a global function with example usage: get_us_dst_start(year) and returns: second_sunday_date