Python - Get Yesterday's date as a string in YYYY-MM-DD format

You Just need to subtract one day from today's date. In Python datetime.timedelta object lets you create specific spans of time as a timedelta object.

datetime.timedelta(1) gives you the duration of "one day" and is subtractable from a datetime object. After you subtracted the objects you can use datetime.strftime in order to convert the result --which is a date object-- to string format based on your format of choice:

>>> from datetime import datetime, timedelta
>>> yesterday = datetime.now() - timedelta(1)

>>> type(yesterday)                                                                                                                                                                                    
>>> datetime.datetime    

>>> datetime.strftime(yesterday, '%Y-%m-%d')
'2015-05-26'

Note that instead of calling the datetime.strftime function, you can also directly use strftime method of datetime objects:

>>> (datetime.now() - timedelta(1)).strftime('%Y-%m-%d')
'2015-05-26'

As a function:

def yesterday(string=False):
    yesterday = datetime.now() - timedelta(1)
    if string:
        return yesterday.strftime('%Y-%m-%d')
    return yesterday

An alternative answer that uses today() method to calculate current date and then subtracts one using timedelta(). Rest of the steps remain the same.

https://docs.python.org/3.7/library/datetime.html#timedelta-objects

from datetime import date, timedelta
today = date.today()
yesterday = today - timedelta(days = 1)
print(today)
print(yesterday)

Output: 
2019-06-14
2019-06-13

>>> import datetime
>>> datetime.date.fromordinal(datetime.date.today().toordinal()-1).strftime("%F")
'2015-05-26'