Get yesterday's date in Python, DST-safe

Question

I have a python script that uses this call to get yesterday\'s date in YYYY-MM-DD format:

str(date.today() - timedelta(days=1)))

It works m

Answer 1

I'm not able to reproduce your issue in python2.7 or python3.2:

>>> import datetime
>>> today = datetime.date(2013, 3, 11)
>>> print today
2013-03-11
>>> day = datetime.timedelta(days=1)
>>> print today - day
2013-03-10

It seems to me that this is already the simplest implementation of a "daylight-savings safe" yesterday() function.

Answer 2

You'll get 2013-03-10 if you use naive datetime object that knows nothing about timezones (and DST in particular):

from datetime import datetime, timedelta

dt_naive = datetime(2013, 3, 11, 0, 35)
print((dt_naive - timedelta(days=1)).date()) # ignores DST
# -> 2013-03-10

2013-03-09 is correct if you are interested what date it was 24 hours ago.

import pytz # $ pip install pytz

local_tz = pytz.timezone("America/Chicago") # specify your local timezone
dt = local_tz.localize(dt_naive, is_dst=None) # raise if dt_naive is ambiguous
yesterday = local_tz.normalize(dt - timedelta(days=1)).date()
print(yesterday)
# -> 2013-03-09

Note: .date() strips timezone info so you'll get 2013-03-10 again:

print(dt.date() - timedelta(days=1))
# -> 2013-03-10

To get yesterday in particular timezone:

from datetime import datetime, time, timedelta
import pytz # $ pip install pytz

tz = pytz.timezone("America/Chicago")
yesterday = datetime.now(tz).date() - timedelta(days=1)

# to add timezone info back (to get yesterday's midnight)
midnight = tz.localize(datetime.combine(yesterday, time(0, 0)), is_dst=None)

Getting yesterday by stripping timezone info might fail if the timezone has missing days around that time. Then this method would produce non-existing date in the given timezone (tz.localize() raises an error).

Answer 3

datetime.date.fromordinal(datetime.date.today().toordinal()-1)