from datetime import timedelta, datetime
import psycopg2
conn = psycopg2.connect("host=bd.ru' port='5432' dbname='bd' user='admin' password='admin'")
cur = conn.cursor()
select_sql = """ select * from table where"""
cur.execute (select_sql)
for row in cur:
    print (row)
cur.close()
conn.commit()
conn.close()

 >>> a=datetime.date(2021, 8, 25)
>>> str(a)
'2021-08-25'

  
>>> import datetime
>>> 
>>> d = datetime.date(2021, 8, 25)
>>> 
>>> out = str(d)
>>> print(out)
2021-08-25
>>> 
>>> out = '{:%Y-%m-%d}'.format(d)
>>> print(out)
2021-08-25
>>>

  
>>> import datetime
>>> 
>>> data = (
...     (datetime.date(2021, 8, 25), 1815061),
...     (datetime.date(2021, 8, 26), 1869308),
...     (datetime.date(2021, 8, 27), 1906561),
...     (datetime.date(2021, 8, 28), 1812178),
...     (datetime.date(2021, 8, 29), 1966867),
...     (datetime.date(2021, 8, 30), 1860015)
... )
>>> 
>>> out = tuple(map(lambda i: (str(i[0]), i[1]), data))
>>> out
(('2021-08-25', 1815061), ('2021-08-26', 1869308), ('2021-08-27', 1906561), ('2021-08-28', 1812178), ('2021-08-29', 1966867), ('2021-08-30', 1860015))
>>>