How to use the black.CannotSplit function in black

def delimiter_split(line: Line, features: Collection[Feature] = ()) -> Iterator[Line]:
    """Split according to delimiters of the highest priority.

    If the appropriate Features are given, the split will add trailing commas
    also in function signatures and calls that contain `*` and `**`.
    """
    try:
        last_leaf = line.leaves[-1]
    except IndexError:
        raise CannotSplit("Line empty")

    bt = line.bracket_tracker
    try:
        delimiter_priority = bt.max_delimiter_priority(exclude={id(last_leaf)})
    except ValueError:
        raise CannotSplit("No delimiters found")

    if delimiter_priority == DOT_PRIORITY:
        if bt.delimiter_count_with_priority(delimiter_priority) == 1:
            raise CannotSplit("Splitting a single attribute from its owner looks wrong")

    current_line = Line(depth=line.depth, inside_brackets=line.inside_brackets)
    lowest_depth = sys.maxsize
    trailing_comma_safe = True

    def append_to_line(leaf: Leaf) -> Iterator[Line]:
        """Append `leaf` to current line or to new line if appending impossible."""
        nonlocal current_line
        try:
            current_line.append_safe(leaf, preformatted=True)
        except ValueError:
            yield current_line

# reported as not fitting a single line.
            yield from right_hand_split(line, line_length, features=features)

        if line.inside_brackets:
            split_funcs = [delimiter_split, standalone_comment_split, rhs]
        else:
            split_funcs = [rhs]
    for split_func in split_funcs:
        # We are accumulating lines in `result` because we might want to abort
        # mission and return the original line in the end, or attempt a different
        # split altogether.
        result: List[Line] = []
        try:
            for l in split_func(line, features):
                if str(l).strip("\n") == line_str:
                    raise CannotSplit("Split function returned an unchanged result")

                result.extend(
                    split_line(
                        l, line_length=line_length, inner=True, features=features
                    )
                )
        except CannotSplit:
            continue

        else:
            yield from result
            break

    else:
        yield line

closing_bracket = None
    for leaf in reversed(line.leaves):
        if current_leaves is body_leaves:
            if leaf is opening_bracket:
                current_leaves = head_leaves if body_leaves else tail_leaves
        current_leaves.append(leaf)
        if current_leaves is tail_leaves:
            if leaf.type in CLOSING_BRACKETS and id(leaf) not in omit:
                opening_bracket = leaf.opening_bracket
                closing_bracket = leaf
                current_leaves = body_leaves
    if not (opening_bracket and closing_bracket and head_leaves):
        # If there is no opening or closing_bracket that means the split failed and
        # all content is in the tail.  Otherwise, if `head_leaves` are empty, it means
        # the matching `opening_bracket` wasn't available on `line` anymore.
        raise CannotSplit("No brackets found")

    tail_leaves.reverse()
    body_leaves.reverse()
    head_leaves.reverse()
    head = bracket_split_build_line(head_leaves, line, opening_bracket)
    body = bracket_split_build_line(body_leaves, line, opening_bracket, is_body=True)
    tail = bracket_split_build_line(tail_leaves, line, opening_bracket)
    bracket_split_succeeded_or_raise(head, body, tail)
    if (
        # the body shouldn't be exploded
        not body.should_explode
        # the opening bracket is an optional paren
        and opening_bracket.type == token.LPAR
        and not opening_bracket.value
        # the closing bracket is an optional paren
        and closing_bracket.type == token.RPAR

current_leaves = head_leaves
    matching_bracket = None
    for leaf in line.leaves:
        if (
            current_leaves is body_leaves
            and leaf.type in CLOSING_BRACKETS
            and leaf.opening_bracket is matching_bracket
        ):
            current_leaves = tail_leaves if body_leaves else head_leaves
        current_leaves.append(leaf)
        if current_leaves is head_leaves:
            if leaf.type in OPENING_BRACKETS:
                matching_bracket = leaf
                current_leaves = body_leaves
    if not matching_bracket:
        raise CannotSplit("No brackets found")

    head = bracket_split_build_line(head_leaves, line, matching_bracket)
    body = bracket_split_build_line(body_leaves, line, matching_bracket, is_body=True)
    tail = bracket_split_build_line(tail_leaves, line, matching_bracket)
    bracket_split_succeeded_or_raise(head, body, tail)
    for result in (head, body, tail):
        if result:
            yield result

Do nothing otherwise.

    A left- or right-hand split is based on a pair of brackets. Content before
    (and including) the opening bracket is left on one line, content inside the
    brackets is put on a separate line, and finally content starting with and
    following the closing bracket is put on a separate line.

    Those are called `head`, `body`, and `tail`, respectively. If the split
    produced the same line (all content in `head`) or ended up with an empty `body`
    and the `tail` is just the closing bracket, then it's considered failed.
    """
    tail_len = len(str(tail).strip())
    if not body:
        if tail_len == 0:
            raise CannotSplit("Splitting brackets produced the same line")

        elif tail_len < 3:
            raise CannotSplit(
                f"Splitting brackets on an empty body to save "
                f"{tail_len} characters is not worth it"

also in function signatures and calls that contain `*` and `**`.
    """
    try:
        last_leaf = line.leaves[-1]
    except IndexError:
        raise CannotSplit("Line empty")

    bt = line.bracket_tracker
    try:
        delimiter_priority = bt.max_delimiter_priority(exclude={id(last_leaf)})
    except ValueError:
        raise CannotSplit("No delimiters found")

    if delimiter_priority == DOT_PRIORITY:
        if bt.delimiter_count_with_priority(delimiter_priority) == 1:
            raise CannotSplit("Splitting a single attribute from its owner looks wrong")

    current_line = Line(depth=line.depth, inside_brackets=line.inside_brackets)
    lowest_depth = sys.maxsize
    trailing_comma_safe = True

    def append_to_line(leaf: Leaf) -> Iterator[Line]:
        """Append `leaf` to current line or to new line if appending impossible."""
        nonlocal current_line
        try:
            current_line.append_safe(leaf, preformatted=True)
        except ValueError:
            yield current_line

            current_line = Line(depth=line.depth, inside_brackets=line.inside_brackets)
            current_line.append(leaf)

# there are no standalone comments in the body
        and not body.contains_standalone_comments(0)
        # and we can actually remove the parens
        and can_omit_invisible_parens(body, line_length)
    ):
        omit = {id(closing_bracket), *omit}
        try:
            yield from right_hand_split(line, line_length, features=features, omit=omit)
            return

        except CannotSplit:
            if not (
                can_be_split(body)
                or is_line_short_enough(body, line_length=line_length)
            ):
                raise CannotSplit(
                    "Splitting failed, body is still too long and can't be split."
                )

            elif head.contains_multiline_strings() or tail.contains_multiline_strings():
                raise CannotSplit(
                    "The current optional pair of parentheses is bound to fail to "
                    "satisfy the splitting algorithm because the head or the tail "
                    "contains multiline strings which by definition never fit one "
                    "line."
                )

    ensure_visible(opening_bracket)
    ensure_visible(closing_bracket)
    for result in (head, body, tail):
        if result:
            yield result

A left- or right-hand split is based on a pair of brackets. Content before
    (and including) the opening bracket is left on one line, content inside the
    brackets is put on a separate line, and finally content starting with and
    following the closing bracket is put on a separate line.

    Those are called `head`, `body`, and `tail`, respectively. If the split
    produced the same line (all content in `head`) or ended up with an empty `body`
    and the `tail` is just the closing bracket, then it's considered failed.
    """
    tail_len = len(str(tail).strip())
    if not body:
        if tail_len == 0:
            raise CannotSplit("Splitting brackets produced the same line")

        elif tail_len < 3:
            raise CannotSplit(
                f"Splitting brackets on an empty body to save "
                f"{tail_len} characters is not worth it"