This does not work:
t = os.path.getmtime(filename)
dTime = datetime.datetime.fromtimestamp(t)
justTime = dTime.timetuple()
if justTime.tm_isdst == 0 :
tDelta = datetime.timedelta(hours=0)
else:
tDelta = datetime.timedelta(hours=1)
What happens instead is that the conditional always equals 1, despite some of the timestamps being within daytime savings time.
I am trying to make a python call match the behavior of a c-based call.
To find out whether a given timestamp corresponds to daylight saving time (DST) in the local time zone:
import os
import time
timestamp = os.path.getmtime(filename)
isdst = time.localtime(timestamp).tm_isdst > 0
It may fail. To workaround the issues, you could get a portable access to the tz database using pytz module:
from datetime import datetime
import tzlocal # $ pip install tzlocal
local_timezone = tzlocal.get_localzone() # get pytz tzinfo
isdst = bool(datetime.fromtimestamp(timestamp, local_timezone).dst())
Related: Use Python to find out if a timezone currently in daylight savings time.
Why do you assume that your filesystem writes down timestamps with a timezone?
On a server, you stick to UTC which does not have DST. On a desktop, you should look up the latest moment of the DST change (on or off), and correct the time accordingly. I don't know if pytz has this information, but this information is definitely available on the web in a machine-readable form.
Note that for some moments during the transition from DST some values of local time occur twice, and it's impossible to tell if a particular timestamp (e.g. 2:30 am) occurred before or after the switch (within an hour).
getmtime() returns "seconds since epoch" that is not in any timezone (it is not in UTC, it is not in the local timezone). It is the same number around the world (it doesn't matter what timezone the server uses as long as its time is synchronized with a desired clock). See Does Python's time.time() return the local or UTC timestamp?
