converting from local to utc timezone

Question

I\'m attempting to craft a function that takes a time object and converts it to UTC time. The code below appears to be off by one hour. When i run noon through the converter,

Answer 1

To convert time in given timezone to UTC time:

from datetime import datetime
import pytz

def convert_to_utc(time, tzname, date=None, is_dst=None):
    tz = pytz.timezone(tzname)
    if date is None: # use date from current local time in tz
        date = datetime.now(tz).date()

    dt = tz.localize(datetime.combine(date, time), is_dst=is_dst)
    return dt.astimezone(pytz.utc).time(), dt.utcoffset().total_seconds()

if is_dst is None it raises an exception for ambiguous local times.

To convert UTC time to local time in given timezone:

def convert_from_utc(time, tzname, date=None):
    tz = pytz.timezone(tzname)
    if date is None: # use date from current time in utc
        date = datetime.utcnow().date()
    dt = datetime.combine(date, time).replace(tzinfo=pytz.utc)
    return tz.normalize(dt.astimezone(tz)).time()

Example:

time = datetime.strptime('12:00:00', "%H:%M:%S").time()
utc_time, offset = convert_to_utc(time, 'America/Chicago')
print utc_time.strftime("%H:%M:%S"), offset # -> 17:00:00 -18000.0

utc_time = datetime.strptime('17:00:00', "%H:%M:%S").time()
time = convert_from_utc(utc_time, 'America/Chicago')
print time.strftime("%H:%M:%S") # -> 12:00:00

In general it is preferable to work with full datetime objects to avoid ambiguity with what is the correct date i.e., pass and return datetime objects.