昨天

from datetime import date, timedelta

yesterday = (date.today() + timedelta(days=-1)).strftime("%Y-%m-%d")
print(yesterday)

今天

from datetime import date, timedelta

today = date.today()
print(today)

明天

from datetime import date, timedelta

tomorrow = (date.today() + timedelta(days= 1)).strftime("%Y-%m-%d")
print(tomorrow)