Creates an "attribute function" for given attribute name(s).

    Resulting function will retrieve attributes with given names, in order,
    from the object that has been passed to it.
    For example, ``attr_func('a', 'b')(foo)`` yields the same as ``foo.a.b``

    :param attrs: Attribute names
    :param default: Optional keyword argument specifying default value
                    that will be returned when some attribute is not present

    :return: Unary attribute function

def attr_func(*attrs, **kwargs):
    """Creates an "attribute function" for given attribute name(s).

    Resulting function will retrieve attributes with given names, in order,
    from the object that has been passed to it.
    For example, ``attr_func('a', 'b')(foo)`` yields the same as ``foo.a.b``

    :param attrs: Attribute names
    :param default: Optional keyword argument specifying default value
                    that will be returned when some attribute is not present

    :return: Unary attribute function
    """
    ensure_argcount(attrs, min_=1)
    ensure_keyword_args(kwargs, optional=('default',))

    # preprocess argument list:
    # * allow dots in arguments, interpreting them as multiple attributes,
    #   e.g. ``attr_func('a.b')`` as ``attr_func('a', 'b')``
    # * make sure the attribute names are valid Python identifiers
    attrs = map(ensure_string, attrs)
    attrs = flatten(attr.split('.') if '.' in attr else [attr]
                    for attr in attrs)
    for attr in attrs:
        if not is_identifier(attr):
            raise ValueError("'%s' is not a valid attribute name", attr)

    if 'default' in kwargs:
        default = kwargs['default']
        if len(attrs) == 1:
            getattrs = lambda obj: getattr(obj, attrs[0], default)
        else:
            def getattrs(obj):
                for attr in attrs:
                    try:
                        obj = getattr(obj, attr)
                    except AttributeError:
                        return default
                return obj
    else:
        if len(attrs) == 1:
            getattrs = operator.attrgetter(attrs[0])
        else:
            def getattrs(obj):
                for attr in attrs:
                    obj = getattr(obj, attr)
                return obj

    return getattrs