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, i get back 18:00:00. But when i run the same data through online converters, i get 17:00:00.

What am i doing wrong here? Any help would be greatly appreciated.

import pytz, datetime

def convert_to_utc(time, tz):
    now_dt = datetime.datetime.utcnow()
    #get a date object
    date_dt = now_dt.date()
    #combine the current date object with our given time object
    dt = datetime.datetime.combine(date_dt, time)
    #get an timezone object for the source timezone
    src_tz = pytz.timezone(str(tz))
    #stamp the source datetime object with the src timezone 
    src_dt = dt.replace(tzinfo=src_tz)
    #get the offset from utc to given timezone
    offset = str(int(src_dt.strftime("%z"))).rstrip('0')
    #convert the source datetime object to
    utc_dt = src_dt.astimezone(pytz.utc)
    #return the converted time and the offset in integer format
    return (utc_dt.time(), int(offset))

time = datetime.datetime.strptime('12:00:00', "%H:%M:%S").time()
(TIME, offset) = convert_to_utc(time, 'America/Chicago')
print TIME.strftime("%H:%M:%S")

**EDIT**

Here's the updated(and functional) code in case anyone else needs help converting to/from UTC.

Thanks everyone for your help!

import pytz, datetime

def convert_to_utc(time, tz): #this returns the offset in int form as well
    now_dt = datetime.datetime.utcnow()
    #get a date object
    date_dt = now_dt.date()
    #combine the current date object with our given time object
    dt = datetime.datetime.combine(date_dt, time)
    #get an timezone object for the source timezone
    src_tz = pytz.timezone(str(tz))
    #stamp the source datetime object with the src timezone 
    src_dt = src_tz.localize(dt)
    #get the offset from utc to given timezone
    offset = str(int(src_dt.strftime("%z"))).rstrip('0')
    #convert the source datetime object to
    utc_dt = src_dt.astimezone(pytz.utc)
    #return the converted time and the offset in integer format
    return (utc_dt.time(), int(offset))

def convert_from_utc(time, tz):
    now_dt = datetime.datetime.now()
    date = now_dt.date()
    dt = datetime.datetime.combine(date, time)
    dest = pytz.timezone(str(tz))
    dt = dt.replace(tzinfo=pytz.utc)
    dest_dt = dt.astimezone(dest)
    return dest_dt.time()

time = datetime.datetime.strptime('12:00:00', "%H:%M:%S").time()
(TIME, offset) = convert_to_utc(time, 'America/Chicago')
print TIME.strftime("%H:%M:%S")

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

Answer 1

Change

src_dt = dt.replace(tzinfo=src_tz)

to

src_dt = src_tz.localize(dt)

Using localize adjusts for Daylight Savings Time, while replace does not. See the section entitled "Localized times and date arithmetic" in the docs.

Answer 2

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.