Fun with Python datetime objects! Works on Python 2.7.x.

python.datetime.fun.py

import datetime
import pytz


def convert_dt_to_milliseconds(dt_obj):
    """Convert  datetime object to a Unix epoch timestamp in milliseconds.

    :param dt_obj: Datetime object to be converted.
    :type dt_obj: instance
    :return: Milliseconds since the Unix epoch.
    :rtype: int or long
    """
    return int((dt_obj - datetime.datetime(1970, 1, 1)).total_seconds() * 1000)


def convert_utc_milliseconds_to_dt(utc_ms):
    """Convert Unix epoch timestamp in milliseconds to a datetime object.

    :param utc_ms: Timestamp in milliseconds.
    :type utc_ms: int or long
    :return: Datetime.datetime() instance.
    :rtype: instance
    """
    return pytz.utc.localize(datetime.datetime.utcfromtimestamp(utc_ms / 1000))


def get_utcnow_in_milliseconds():
    """Get the current UTC time and convert it to a Unix epoch timestamp in milliseconds.

    :return: Milliseconds since the Unix epoch.
    :rtype: int or long
    """
    return int((datetime.datetime.utcnow() - datetime.datetime(1970, 1, 1)).total_seconds() * 1000)


def get_utcnow_date_str(datetime_obj=None):
    """Get the date in ISO format.

    :param datetime_obj: (optional) If specified, returns the ISO format of the `datetime` instance.
                         (default: None)
    :type datetime_obj: datetime.datetime, datetime.date
    :return: Date string.
    :rtype: str
    """
    if datetime_obj is None:
        datetime_obj = datetime.datetime.utcnow()
    return datetime_obj.date().isoformat()


def convert_local_dt_to_utc_dt(local_dt):
    """Convert local `datetime.datetime` instance to UTC.

    :param local_dt: Local `datetime.datetime` instance.
    :type local_dt: datetime.datetime
    :return: UTC `datetime.datetime` instance.
    :rtype: datetime.datetime
    """
    if time.daylight:
        offset = time.altzone / 3600
    else:
        offset = time.timezone / 3600
    return local_dt + datetime.timedelta(hours=offset)


def datetime_utc_to_timezone_traverse(obj, path=None, callback=None, convert_to_tz=None):
    """Recursively looks for a key in a dictionary and returns the value, if found.

    convert_to_tz='US/Pacific'

    :param obj: Dictionary to iterate through.
    :return: Result or None.
    :rtype: str, unicode, int, float, long, or NoneType
    """
    # TODO: Fix this docstring.

    if path is None:
        path = []

    if isinstance(obj, dict):
        value = {k: datetime_utc_to_timezone_traverse(v, path + [k], callback, convert_to_tz) for k, v in obj.items()}
    elif isinstance(obj, (list, set)):
        value = [datetime_utc_to_timezone_traverse(elem, path + [[]], callback, convert_to_tz) for elem in obj]
    elif isinstance(obj, (datetime.datetime, datetime.time)):
        # value = obj.replace(tzinfo=pytz.utc)

        # TODO: Add checking to see if a timezone is already set then localize if not else obj.astimezone(...)
        # value = pytz.utc.localize(obj).astimezone(pytz.timezone(convert_to_tz))

        value = obj.astimezone(pytz.timezone(convert_to_tz))
    else:
        value = obj

    if callback is None:  # if a callback is provided, call it to get the new value
        return value
    else:
        return callback(path, value)


def timestamp_to_str_traverse(obj, path=None, callback=None):
    """Recursively looks for datetime objects and converts them to ISO formatted strings.

    :param obj: Dictionary to iterate through.
    :param key: Key to look for.
    :return: Result or None.
    :rtype: str, unicode, int, float, long, or NoneType
    """
    # TODO: Fix this docstring.

    if path is None:
        path = []

    if isinstance(obj, dict):
        value = {k: timestamp_to_str_traverse(v, path + [k], callback) for k, v in obj.items()}
    elif isinstance(obj, (list, set)):
        value = [timestamp_to_str_traverse(elem, path + [[]], callback) for elem in obj]
    else:
        if isinstance(obj, (datetime.datetime, datetime.date, datetime.time)):
            obj.isoformat()
        else:
            value = obj

    if callback is None:  # if a callback is provided, call it to get the new value
        return value
    else:
        return callback(path, value)

    
# Thanks ZenDesk -- Convert "2016-10-10T14:21:54Z" to datetime object.
import re
regex_timestamp_zendesk = re.compile('^[0-9]{4}-[0-9]{2}-[0-9]{2}T[0-9]{2}:[0-9]{2}:[0-9]{2}[A-Za-z]+$')
regex_timestamp_iso = re.compile('^[0-9]{4}-[0-9]{2}-[0-9]{2}T[0-9]{2}:[0-9]{2}:[0-9]{2}$')
regex_timestamp_iso_tz = re.compile('^[0-9]{4}-[0-9]{2}-[0-9]{2}T[0-9]{2}:[0-9]{2}:[0-9]{2}\.{0,1}[0-9]*[+\-][0-9]{2}:?[0-9]{2}$')
regex_timestamp_ms = re.compile('\.\d+')

def timestamp_to_datetime_traverse(obj, path=None, callback=None, convert_to_tz=None):
    """Recursively looks for a key in a dictionary and returns the value, if found.

    convert_to_tz='US/Pacific'

    :param obj: Dictionary to iterate through.
    :param key: Key to look for.
    :return: Result or None.
    :rtype: str, unicode, int, float, long, or NoneType
    """
    # TODO: Fix this docstring.

    if path is None:
        path = []

    if isinstance(obj, dict):
        value = {k: timestamp_to_datetime_traverse(v, path + [k], callback, convert_to_tz) for k, v in obj.items()}
    elif isinstance(obj, (list, set)):
        value = [timestamp_to_datetime_traverse(elem, path + [[]], callback, convert_to_tz) for elem in obj]
    else:
        if isinstance(obj, (str, unicode)):
            # Convert '2017-10-04T21:09:43.717000Z' to '2017-10-04T21:09:43Z'
            if '.' in obj and obj.endswith('Z'):
                obj_split = obj.split('.')
                obj = '{}Z'.format(obj_split[0])

            if regex_timestamp_zendesk.match(obj):
                value = pytz.utc.localize(datetime.datetime.strptime(obj, '%Y-%m-%dT%H:%M:%SZ'))
                if convert_to_tz:
                    value = value.astimezone(pytz.timezone(convert_to_tz))
            elif regex_timestamp_iso.match(obj):
                value = pytz.utc.localize(datetime.datetime.strptime(obj, '%Y-%m-%dT%H:%M:%S'))
                if convert_to_tz:
                    value = value.astimezone(pytz.timezone(convert_to_tz))
            elif regex_timestamp_iso_tz.match(obj):
                # The Python 2 strptime() function indeed does not the support %z format for timezones
                # (because the underlying time.strptime() function doesn't support it) so skip it.
                # TODO: Add support for determining the timezone just in-case some wise-ass isn't using UTC...
                if obj.endswith('00:00'):
                    value = pytz.utc.localize(datetime.datetime.strptime(obj[:19], '%Y-%m-%dT%H:%M:%S'))
                    if convert_to_tz:
                        value = value.astimezone(pytz.timezone(convert_to_tz))
                elif obj.endswith(':00'):
                    # obj = re.sub('\.\d+', '', obj)
                    obj = regex_timestamp_ms.sub('', obj)
                    # THIS SHOULD REMEDY THE TO-DO FROM ABOVE...
                    ret = datetime.datetime.strptime(obj[0:18], '%Y-%m-%dT%H:%M:%S')
                    if obj[19] == '+':
                        ret -= datetime.timedelta(hours=int(obj[20:22]), minutes=int(obj[23:]))
                    elif obj[19] == '-':
                        ret += datetime.timedelta(hours=int(obj[20:22]), minutes=int(obj[23:]))
                    value = pytz.utc.localize(ret)
                    if convert_to_tz:
                        value = value.astimezone(pytz.timezone(convert_to_tz))
                else:
                    value = pytz.utc.localize(datetime.datetime.strptime(obj, '%Y-%m-%dT%H:%M:%SZ'))
                    if convert_to_tz:
                        value = value.astimezone(pytz.timezone(convert_to_tz))
            else:
                value = obj
        else:
            value = obj

    if callback is None:  # if a callback is provided, call it to get the new value
        return value
    else:
        return callback(path, value)