from datetime import datetime


def datetime_unserializer(d_str):
    """Convert a string representation to a datetime object for JSON unserialization.
    
    :param d_str: the datetime string we want to unserialize
    :type d_str: str
    
    :return: the datetime unserialized to a datetime
    :rtype: datetime
    """
    return datetime.fromisoformat(d_str)