def full_class_name(o):
    """
    Returns the full qualified name of the class of o.

    :param o: The object whose class name should be returned
    :return: A str representing the class of o
    :rtype: str
    """
    module = o.__class__.__module__
    if module is None or module == str.__class__.__module__:
        return o.__class__.__name__
    else:
        return module + '.' + o.__class__.__name__
