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?