Convert a ISO 8601 formatted datetime string to a python datetime. Supports basic and extended ISO 8601 formatting.

datetime_from_iso.py

import re
from datetime import datetime, timedelta
from decimal import Decimal

def datetime_from_iso(text):
    '''
    Convert a ISO 8601 formatted datetime string to a python datetime
    NOTE: this function is intentionally *not* timezone-aware; providing timezone information beyond 'Z' will fail.
    NOTE: the parsing is sligthly too permissive; you can mix and match basic and extended ISO 8601 formatting (could be solved by using two regexes instead of one).
    '''
    m = re.match(r'(?P<year>\d{4})-?(?P<month>\d{2})-?(?P<day>\d{2})(T(?P<hours>\d{2})(:?(?P<minutes>\d{2})(:?(?P<seconds>\d{2}))?)?([,.](?P<fractional>\d+))?Z?)?', text)
    # only keep fields that are present in the input text
    data = {k: int(v) for k, v in m.groupdict().items() if v is not None}
    # handle fractional time part
    if 'fractional' in data:
        if 'seconds' in data:
            # fractional seconds
            data['microseconds'] = int(str(data['fractional']).ljust(6, '0'))
        elif 'minutes' in data:
            # fractional minutes
            value = Decimal('0.' + str(data['fractional'])) * 60  # minutes to seconds
            data['seconds'] = int(value)
            if value != int(value):
                data['microseconds'] = int((value - int(value))*10**6)
        else:
            # fractional hours
            value = Decimal('0.' + str(data['fractional'])) * 60  # hours to minutes
            data['minutes'] = int(value)
            if value != int(value):
                value = (value - int(value)) * 60  # minutes to seconds
                data['seconds'] = int(value)
                if value != int(value):
                    data['microseconds'] = int((value - int(value))*10**6)
    return datetime(
        data.get('year', 0),
        data.get('month', 0),
        data.get('day', 0),
        data.get('hours', 0),
        data.get('minutes', 0),
        data.get('seconds', 0),
        data.get('microseconds', 0),
    )