Utilities to assist with ASCII art such as railroad diagrams; since these use Unicode box drawing characters and are better for diagrams such as railroad diagrams, this is neither ASCII nor art.

Latest release 20260228: Initial release. Basic railroad diagrams and associated utilities.

This is still pretty alpha.

The current demo mode runs:

rrprint(
    RR_START,
    RRRepeat("repeat me"),
    "2 lines\naaaa",
    (
        "one",
        "two",
        "three",
        "one\n"
        "two\n"
        "three\n"
        "four\n"
        "five",
        ["a", "sequence"],
    ),
    RR_END,
)

which prints:

                              ╭|one|──────────╮
                              ├|two|──────────┤
                              ├|three|────────┤
                   ╭───────╮  │╭─────╮        │
                   │2 lines│  ││one  │        │
├┼──┬|repeat me|┬──┤aaaa   ├──┤│two  │        ├──┼┤
    ╰─────←─────╯  ╰───────╯  ├┤three├────────┤
                              ││four │        │
                              ││five │        │
                              │╰─────╯        │
                              ╰|a|──|sequence|╯

Short summary:

• box_char: Return the Unicode entity for a box drawing glyph with the specified line weight and lines.
• box_char_name: Compute the Unicode entity name for a box drawing glyph with the specified line weight and lines.
• Cell: A representation of a character cell for a hypothetical future "drawing on a canvas" mode.
• render: A decorator to wrap rendering methods with the prevailing render context, as updated by any keyword arguments supplied to the method.
• render_mode: A context manager to temporarily apply render_kw to the rendering mode context ctx (default from RRBase.render_context). Yields the render context.
• RR_END: A bare text based symbol like RR_START or RR_END.
• RR_START: A bare text based symbol like RR_START or RR_END.
• RRBase: The abstract base class for various boxes.
• RRChoice: RRChoice(content: list[cs.ascii_art.RRBase] = ).
• RRMerge: RRMerge multiple inputs into a single output.
• RROptional: RROptional(content: cs.ascii_art.RRBase, above: bool = False, middle: str = '→').
• rrprint: Promote the arguments to RRBase instances, make into an RRSequence and print it.
• RRRepeat: RRRepeat(content: cs.ascii_art.RRBase, above: bool = False, middle: str = '←').
• RRSequence: A railroad sequence.
• RRSplit: RRSplit a single input into multiple outputs.
• RRStack: An unadorned vertical stack of the content.
• RRTextBox: A text box with borders.
• Symbol: A bare text based symbol like RR_START or RR_END.
• Terminal: Like a symbol, but with a marker either side.
• test_railroad: Exercise various boxes.

Module contents:

• box_char(heavy=False, *, arc=None, ascii=None, up=False, down=False, left=False, right=False, render_mode=None): Return the Unicode entity for a box drawing glyph with the specified line weight and lines.

  Parameters:

  • arc: return an arc character instead of a rectangluar box corner
  • ascii: use ASCII characters rather than Unicode box drawing characters
  • heavy: the line wieght: HEAVY for True, LIGHT for False
  • up: with a line upward from the centre
  • down: with a line downward from the centre
  • left: with a line leftward from the centre
  • right: with a line rightward from the centre

• box_char_name(heavy=False, arc=False, up=False, down=False, left=False, right=False): Compute the Unicode entity name for a box drawing glyph with the specified line weight and lines.

  See: https://www.unicode.org/charts/nameslist/n_2500.html

  Parameters:

  • arc: return an arc character instead of a rectangluar box corner
  • heavy: the line wieght: HEAVY for True, LIGHT for False
  • up: with a line upward from the centre
  • down: with a line downward from the centre
  • left: with a line leftward from the centre
  • right: with a line rightward from the centre

• class Cell: A representation of a character cell for a hypothetical future "drawing on a canvas" mode.

• render(*da, **dkw): A decorator to wrap rendering methods with the prevailing render context, as updated by any keyword arguments supplied to the method.

  The decorator may be suplied with its own defaults; these will be applied to the render context first, then whatever render keyword arguments as supplied to the method.

  The decorated method accepts an optional ctx parameter to use as the render context; the default comes from self.render_context which is normally an attribute of self.__class__.

  The wrapped method is called with a keyword argument for every attribute of the updated render context. The render context is returned to its previous state on return from the method.

  This means that the render methods have an unusual signature, for example:

  @render(heavy=True)
  def renderlines(self, *, heavy, attach_w, attach_e, **_):
  

  This:

  • enumerates only the keyword parameters of interest to the method
  • "default" values should not be supplied as None in the method definition
  • has a _ to collect any uninteresting render parameters

  The interesting parameters should arrive prefilled and also do not need to be passed into interior calls to render methods because the render context has these values. Only values different from the render context need provision.

• render_mode(ctx=None, **render_kw): A context manager to temporarily apply render_kw to the rendering mode context ctx (default from RRBase.render_context). Yields the render context.

• RR_END = Symbol:'┼┤': A bare text based symbol like RR_START or RR_END.

• RR_START = Symbol:'├┼': A bare text based symbol like RR_START or RR_END.

• class RRBase(cs.deco.Promotable): The abstract base class for various boxes.

RRBase.__str__(self): Return the default rendering of the text box.

RRBase.conn_char(li, lefts: list[int], rights: list[int], arc=True, heavy=False) -> str: Compute the connective box_char for a column of connective characters.

RRBase.from_str(s: str) -> Union[ForwardRef('Terminal'), ForwardRef('RRTextBox')]: Promote a string to a Terminal or RRTextBox. Nonempty strings with no newlines become Terminals, otherwise a RRTextBox.

RRBase.horiz(width: int, *, middle='', arc, heavy, ascii=False, left_up=False, left_down=False, right_up=False, right_down=False, **_): Compute a horizontal line with an optional symbol in the middle and up or down connections.

RRBase.pprint(self, **ppkw): Call pprint.pprint with this railroad node.

RRBase.render(self, **render_kw): Render the text box as a single multiline string.

RRBase.render_lines(self, **render_kw): Render the box as a list of single line strings.

• class RRChoice(RRStack): RRChoice(content: list[cs.ascii_art.RRBase] = )
• class RRMerge(RRStack): RRMerge multiple inputs into a single output.

RRMerge.e: The east attachment points of the RRMerge, the midpoint of the interior top and bottom attachment points.

RRMerge.es: The east attachment points of the RRMerge, the midpoint of the interior top and bottom attachment points.

RRMerge.render_lines(self, *, arc, heavy, attach_e, **_): Render the RRMerge as a list of strings.

RRMerge.width: The width of the RRMerge, the width of the RRStack plus 1 for the right attachments.

• class RROptional(_RailRoadAround): RROptional(content: cs.ascii_art.RRBase, above: bool = False, middle: str = '→')
• rrprint(*seq, sep=''): Promote the arguments to RRBase instances, make into an RRSequence and print it.
• class RRRepeat(_RailRoadAround): RRRepeat(content: cs.ascii_art.RRBase, above: bool = False, middle: str = '←')
• class RRSequence(_RailRoadMulti): A railroad sequence.

RRSequence.height: The render height ofthe RRSequence in lines.

RRSequence.render_lines(self, *, sep_len, middle='', **_): Render the RRSequence as a list of one line strings.

RRSequence.width: The render width of the RRSequence in characters..

• class RRSplit(RRStack): RRSplit a single input into multiple outputs.

RRSplit.render_lines(self, *, arc, heavy, attach_w, **_): Render the RRSplit as a list of strings.

RRSplit.w: The west attachment point, the midpoint of the top and bottom interior west attachment points.

RRSplit.width: The width of the RRSplit in characters.

RRSplit.ws: The west attachment points of the RRSplit.

• class RRStack(_RailRoadMulti): An unadorned vertical stack of the content.

RRStack.width: The overall width of the content.

• class RRTextBox(RRBase): A text box with borders.

RRTextBox.e: The vertical offset to the east connection point.

RRTextBox.height: The height including the borders

RRTextBox.n: The horizontal offset to the north connection point.

RRTextBox.render_lines(self, *, heavy, attach_w, attach_e, **_): Render the text box as a list of single line strings.

RRTextBox.s: The horizontal offset to the south connection point.

RRTextBox.w: The vertical offset to the west connection point.

RRTextBox.width: The width including the borders

• class Symbol(RRBase): A bare text based symbol like RR_START or RR_END.
• class Terminal(Symbol): Like a symbol, but with a marker either side.
• test_railroad(): Exercise various boxes.

Release Log

Release 20260228: Initial release. Basic railroad diagrams and associated utilities.