<human>:  change date into string.
<bot>: Here is a Python function to change date into string

import datetime

def _change_date_into_string(date):
 """Change date into string"""
 return date.strftime("%Y-%m-%d")

# Enter the date
date = datetime.date(2018, 1, 1)

# Calling the function
print((_change_date_into_string(date)))

#Example Output
# 2018-01-01

#Remember to inspect code for bugs.