Python strptime - Handling single digit dates

Question

I've been working on trying to convert a given time to a different format, taking into account an external device's timezone, skipping the OS's timezone conversions.

Initially, I have a time in UTC seconds, and the timezone from the device. For example, where I am right now the time is seconds=1343931446, and timezone = -0700. What I'm trying to do is convert this to the format YYYYMMDD_HHMMSS, which has worked properly for a while. For the above values, it should come out to be 20120802_111726.

This following block of code worked since I wrote it, conveniently on July 11th. The issue comes down to the fact that when the day is only 1 digit long (aka starting yesterday), the parsing goes wrong, and I get 20120821_011726. I'm presuming the issue is when I convert the time value into date time, as when I print time_t, I'll get time.struct_time(tm_year=2012, tm_mon=8, tm_mday=2, tm_hour=18, tm_min=17, tm_sec=26, tm_wday=3, tm_yday=215, tm_isdst=0), which is treated as single character strings when parsed into a datetime.

The question is, can I force datetime to accept a 2-character input for the day of the month/hour so it will parse properly, or is there a better way of transforming these formats? Keep in mind that this current method was written due to not being able to use any methods that account for the current system time, as this is done where the time zone is not guaranteed to be same on the system as the device that the seconds were obtained from.

def convert_time(seconds, tz):
    """ Times obtained were in seconds since epoch. 
        Convert to format YYYYMMDD_HHMMSS.
    """
    time_t = time.gmtime(seconds) # convert to time tuple
    # convert to datetime format - because time zone comparisons can't be made
    # in a format directly convertible from UTC
       time_dt = datetime.datetime.strptime(str(time_t.tm_year) + 
                                            str(time_t.tm_mon)  + 
                                            str(time_t.tm_mday) +
                                            str(time_t.tm_hour) + 
                                            str(time_t.tm_min)  + 
                                            str(time_t.tm_sec), 
                                            '%Y%m%d%H%M%S')

    # Convert time zone to timedelta
    offset = datetime.timedelta(hours=int(tz.lstrip('-')[:2]), 
                                minutes=int(tz.lstrip('-')[2:]))
    sign = -1 if tz.startswith('-') else 1
    time_dt = time_dt + sign * offset
    time_dt = time_dt.strftime('%Y%m%d_%H%M%S')

    return time_dt

Answer 1

Your timestamp is expressed in seconds, your timezone in hours and minutes. Simply subtract or add the timezone converted to seconds, then use the time.strftime function to format that to the string you want:

def convertTime(seconds, tz):
    tzhours, tzminutes = map(int, (tz.lstrip('-')[:2], tz[-2:]))
    offset = tzhours * 3600 + tzminutes * 60
    if tz.startswith('-'):
        offset *= -1
    return time.strftime('%Y%m%d_%H%M%S', time.gmtime(seconds + offset))