[Python] Python pass tzinfo to naive datetime without pytz

I've been struggling for way too long on dates/timezones in Python and was thinking someone could give me a hand here.

Basically I want to do a conversion in UTC and taking into account DST changes.

I've created the following tzinfo class from one of the Python tutorials (not 100% accurate I know but it doesn't need to):

from datetime import tzinfo, timedelta, datetime

ZERO = timedelta(0)
HOUR = timedelta(hours=1)

def first_sunday_on_or_after(dt):
days_to_go = 6 - dt.weekday()
if days_to_go:
dt += timedelta(days_to_go)
return dt

DSTSTART_2007 = datetime(1, 3, 8, 2)
DSTEND_2007 = datetime(1, 11, 1, 1)
DSTSTART_1987_2006 = datetime(1, 4, 1, 2)
DSTEND_1987_2006 = datetime(1, 10, 25, 1)
DSTSTART_1967_1986 = datetime(1, 4, 24, 2)
DSTEND_1967_1986 = DSTEND_1987_2006

class USTimeZone(tzinfo):

def __init__(self, hours, reprname, stdname, dstname):
self.stdoffset = timedelta(hours=hours)
self.reprname = reprname
self.stdname = stdname
self.dstname = dstname

def __repr__(self):
return self.reprname

def tzname(self, dt):
if self.dst(dt):
return self.dstname
else:
return self.stdname

def utcoffset(self, dt):
return self.stdoffset + self.dst(dt)

def dst(self, dt):
if dt is None or dt.tzinfo is None:
# An exception may be sensible here, in one or both cases.
# It depends on how you want to treat them. The default
# fromutc() implementation (called by the default astimezone()
# implementation) passes a datetime with dt.tzinfo is self.
return ZERO
assert dt.tzinfo is self

# Find start and end times for US DST. For years before 1967, return
# ZERO for no DST.
if 2006 < dt.year:
dststart, dstend = DSTSTART_2007, DSTEND_2007
elif 1986 < dt.year < 2007:
dststart, dstend = DSTSTART_1987_2006, DSTEND_1987_2006
elif 1966 < dt.year < 1987:
dststart, dstend = DSTSTART_1967_1986, DSTEND_1967_1986
else:
return ZERO

start = first_sunday_on_or_after(dststart.replace(year=dt.year))
end = first_sunday_on_or_after(dstend.replace(year=dt.year))

# Can't compare naive to aware objects, so strip the timezone from
# dt first.
if start <= dt.replace(tzinfo=None) < end:
return HOUR
else:
return ZERO


On the other side I have an arbitrary date object in EST, and I want to know the number of hours they differ by taking into account DST.

I've tried something like this:

>>> Eastern = ustimezone.USTimeZone(-5, "Eastern", "EST", "EDT")
>>> x = datetime.date.today() # I actually get an arbitrary date but this is for the example
>>> x_dt = datetime.datetime.combine(x, datetime.time())
>>> x_dt_tz = x_dt.astimezone(Eastern)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
ValueError: astimezone() cannot be applied to a naive datetime


I've seen several posts who tell to use localize from the pytz module, but unfortunately I am not able to use additional modules, so impossible to use pyzt

Does anyone know how I can get this naive datetime into a timezoned object without using pytz?

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