generalized_time_to_datetime.py

""" Tool function to convert Generalized Time string
    to Python datetime object
"""

import datetime
import pytz

def gt_to_dt(gt):
    """ Convert GeneralizedTime string to python datetime object

        >>> gt_to_dt("20150131143554.230")
        datetime.datetime(2015, 1, 31, 14, 35, 54, 230)
        >>> gt_to_dt("20150131143554.230Z")
        datetime.datetime(2015, 1, 31, 14, 35, 54, 230, tzinfo=<UTC>)
        >>> gt_to_dt("20150131143554.230+0300")
        datetime.datetime(2015, 1, 31, 11, 35, 54, 230, tzinfo=<UTC>)
    """
    # check UTC and offset from local time
    utc = False
    if "Z" in gt.upper():
        utc = True
        gt = gt[:-1]
    if gt[-5] in ['+', '-']:
        # offsets are given from local time to UTC, so substract the offset to get UTC time
        hour_offset, min_offset = -int(gt[-5] + gt[-4:-2]), -int(gt[-5] + gt[-2:])
        utc = True
        gt = gt[:-5]
    else:
        hour_offset, min_offset = 0, 0

    # microseconds are optionnals
    if "." in gt:
        microsecond = int(gt[gt.index('.') + 1:])
        gt = gt[:gt.index('.')]
    else:
        microsecond = 0

    # seconds and minutes are optionnals too
    if len(gt) == 14:
        year, month, day, hours, minutes, sec = int(gt[:4]), int(gt[4:6]), int(gt[6:8]), int(gt[8:10]), int(gt[10:12]), int(gt[12:])
        hours += hour_offset
        minutes += min_offset
    elif len(gt) == 12:
        year, month, day, hours, minutes, sec = int(gt[:4]), int(gt[4:6]), int(gt[6:8]), int(gt[8:10]), int(gt[10:]), 0
        hours += hour_offset
        minutes += min_offset
    elif len(gt) == 10:
        year, month, day, hours, minutes, sec = int(gt[:4]), int(gt[4:6]), int(gt[6:8]), int(gt[8:]), 0, 0
        hours += hour_offset
        minutes += min_offset
    else:
        # can't be a generalized time
        raise ValueError('This is not a generalized time string')

    # construct aware or naive datetime
    if utc:
        dt = datetime.datetime(year, month, day, hours, minutes, sec, microsecond, tzinfo=pytz.UTC)
    else:
        dt = datetime.datetime(year, month, day, hours, minutes, sec, microsecond)
    # done !
    return dt