snaptui 0.2.0

Minimal Python Charm stack — raw terminal TUI framework

snaptui

A zero-dependency Python TUI framework that ports the Charm stack's approach to terminal UIs: the Elm Architecture, raw terminal I/O, and ANSI escape sequences.

Why this exists

Python's TUI options are either curses-based (complex, stateful, platform-dependent) or heavy frameworks like Textual (hundreds of dependencies, CSS layout engine, async runtime). The Go ecosystem solved this with the Charm stack: a set of composable libraries that render TUIs by writing ANSI escape sequences directly to stdout. This makes rendering fast and the architecture simple -- your entire UI is a function that returns a string.

snaptui brings that approach to Python:

• No curses. Reads raw bytes from stdin, writes ANSI sequences to stdout.
• No dependencies. Uses only the Python standard library (termios, select, signal, fcntl).
• Elm Architecture. Your app is init(), update(msg), view() -- nothing else.
• Fast rendering. A line-diff renderer only redraws what changed, just like Bubble Tea.

How the Elm Architecture works

from snaptui import Model, Cmd, KeyMsg, WindowSizeMsg, quit_cmd

class Counter:
    def __init__(self):
        self.count = 0

    def init(self) -> Cmd:
        return None

    def update(self, msg) -> tuple['Counter', Cmd]:
        if isinstance(msg, KeyMsg):
            if msg.key == 'q':
                return self, quit_cmd
            elif msg.key == 'up':
                self.count += 1
            elif msg.key == 'down':
                self.count -= 1
        return self, None

    def view(self) -> str:
        return f"Count: {self.count}\n\nup/down to change, q to quit"

The program calls view() after every update(), diffs the output, and writes only the changed lines. There's no widget tree, no layout engine, no virtual DOM -- just a string.

Why escape sequences make this fast

Traditional TUI frameworks (curses, Textual) maintain an internal screen buffer and compute cell-by-cell diffs. snaptui skips all of that:

1. Your view() returns a string with embedded ANSI codes for colors, bold, etc.
2. The renderer splits it into lines and compares against the previous frame.
3. Only changed lines get written using cursor-movement escape sequences.
4. One flush() per frame -- the terminal handles the rest.

Because ANSI rendering is done by the terminal emulator (which is GPU-accelerated in modern terminals like Ghostty, Kitty, WezTerm), the Python side only needs to produce and diff strings. There's no pixel math, no redraw-the-whole-screen, no intermediate buffer.

Why not cell-level diffing?

Bubble Tea v2 introduced a "Cursed Renderer" that parses view output through an ANSI state machine, builds a 2D grid of cells (each with character + style attributes), and diffs individual cells against the previous frame. snaptui deliberately does not adopt this approach.

The reason is the ratio of computation cost to I/O savings. In Go, the ANSI parser is compiled machine code -- iterating 80x40 = 3,200 cells, comparing structs, and building output takes microseconds. The I/O savings (writing 200 bytes instead of 3,000) are worth more than the computation cost.

In Python, the same state-machine parser would iterate character-by-character through interpreted code, create objects for each cell, and do attribute comparisons through Python's object protocol. For 3,200 cells this easily costs 1-5ms, while the I/O savings of ~2,800 fewer bytes is maybe 0.1ms at TTY write speeds. You'd spend 5ms of CPU to save 0.1ms of I/O.

The line-diff renderer sidesteps this: string equality (old == new) is a single C-level comparison in CPython. No parsing, no cell objects, no per-character work. The cost is near-zero, and unchanged lines (the majority of the screen on any given frame) are skipped entirely.

What's ported from where

snaptui combines features from four Charm libraries into one package, porting from these exact versions:

Go module	Version
charmbracelet/bubbletea	v1.3.10
charmbracelet/lipgloss	v1.1.0
charmbracelet/bubbles	v1.0.0
charmbracelet/huh	v0.8.0
charmbracelet/x/ansi	v0.11.6

Here's what's implemented and what's not:

Core Framework

Feature	Charm Source	snaptui	Status
Elm Architecture (init/update/view)	bubbletea	Model protocol, Program	Done
Message types (Key, WindowSize, Quit)	bubbletea	KeyMsg, WindowSizeMsg, QuitMsg	Done
Command system (async Cmd)	bubbletea	Cmd, batch(), quit_cmd	Done
Raw terminal mode (termios)	bubbletea	terminal.make_raw()	Done
Alternate screen buffer	bubbletea	Program(alt_screen=True)	Done
Line-diff renderer	bubbletea	renderer.Renderer	Done
Keyboard input parsing (70+ sequences)	bubbletea	keys.read_key()	Done
SIGWINCH resize handling	bubbletea	terminal.listen_for_resize()	Done
Mouse input events	bubbletea	--	Not yet
Bracketed paste events	bubbletea	--	Not yet
Declarative View struct (cursor, title, alt screen)	bubbletea v2	View dataclass	Done
Key modifier bitfield	bubbletea v2	Mod IntFlag on KeyMsg	Done
Focus/blur events	bubbletea v2	--	Not yet
Kitty keyboard protocol	bubbletea v2	--	Not yet
Clipboard (OSC 52)	bubbletea v2	--	Not yet
Subscriptions (long-running listeners)	bubbletea	--	Not yet
Suspend/resume (Ctrl+Z)	bubbletea	--	Not yet

Styling

Feature	Charm Source	snaptui	Status
Chainable style builder	lipgloss	Style class	Done
Text attributes (bold, dim, italic, underline, reverse, strikethrough)	lipgloss	Style.bold(), .dim(), etc.	Done
Underline styles (curly, dotted, dashed, double) and color	lipgloss v2	Style.underline_style(), .underline_color()	Done
True color (24-bit RGB)	lipgloss	Style.fg(), .bg()	Done
Padding (CSS shorthand)	lipgloss	Style.padding()	Done
Margin (CSS shorthand)	lipgloss	Style.margin()	Done
Width/height constraints	lipgloss	Style.width(), .height()	Done
Max width/height	lipgloss	Style.max_width(), .max_height()	Done
Auto word-wrap on .width()	lipgloss	Style._apply_wrap()	Done
Borders (5 types, per-side, colored)	lipgloss	Style.border(), .border_fg()	Done
Horizontal alignment	lipgloss	Style.align()	Done
Immutable builder pattern	lipgloss	Style._copy()	Done
ANSI 16/256 color fallback	lipgloss	--	Not yet
Adaptive colors (light/dark)	lipgloss	--	Not yet
Vertical alignment	lipgloss	--	Not yet
Tab width	lipgloss	--	Not yet
Table rendering	lipgloss/table	--	Not yet
List rendering (enumerators)	lipgloss/list	--	Not yet
Tree rendering	lipgloss/tree	--	Not yet

Layout

Feature	Charm Source	snaptui	Status
Join blocks horizontally	lipgloss	join_horizontal()	Done
Join blocks vertically	lipgloss	join_vertical()	Done
Place content in canvas (2D)	lipgloss	place()	Done
PlaceHorizontal / PlaceVertical	lipgloss	--	Not yet

String Utilities

Feature	Charm Source	snaptui	Status
ANSI-aware visible width	x/ansi	strutil.visible_width()	Done
ANSI stripping	x/ansi	strutil.strip_ansi()	Done
ANSI-aware truncation	x/ansi	strutil.truncate()	Done
ANSI-aware word wrap	x/ansi	strutil.word_wrap()	Done
ANSI-aware padding	x/ansi	strutil.pad_right()	Done
CJK wide character support	x/ansi	strutil._char_width()	Done
Grapheme cluster segmentation	x/ansi	--	Not yet
Hard wrap (non-word-boundary)	x/ansi	--	Not yet (hard-break exists within word_wrap)
Truncate with tail ("...")	x/ansi	--	Not yet

Components

Component	Charm Source	snaptui	Status
Single-line text input	bubbles/textinput	TextInput	Done
Multi-line text area	bubbles/textarea	TextArea	Done
Scrollable viewport	bubbles/viewport	Viewport	Done
Paginated list (delegate pattern)	bubbles/list + bubbles/paginator	List	Done
Option picker (select)	bubbles/list	Select	Done
Yes/No confirmation	huh	Confirm	Done
Multi-field form	huh	Form	Done
Form theme (focused/blurred styles)	huh	Theme, ThemeCharm	Done
App theme (titles, borders, list items)	snaptui-original	AppTheme, AppThemeCharm	Done
Table	bubbles/table	--	Not yet
Spinner	bubbles/spinner	--	Not yet
Progress bar	bubbles/progress	--	Not yet
File picker	bubbles/filepicker	--	Not yet
Timer / Stopwatch	bubbles/timer, bubbles/stopwatch	--	Not yet
Help (auto-generated keybinds)	bubbles/help	--	Not yet

Legend

• Done -- Implemented and tested
• Not yet -- Not implemented; listed here so future apps know what to add when they need it

Architecture

your_app.py
    |
    +-- snaptui (framework + styling + components in one package)
            |
            +-- model.py        Elm Architecture: Model protocol, Msg, Cmd
            +-- keys.py         Keyboard input: escape sequence parser
            +-- program.py      Event loop: raw mode, resize, render cycle
            +-- terminal.py     Low-level: termios, ioctl, ANSI sequences
            +-- renderer.py     Line-diff screen updates
            +-- style.py        Lip Gloss equivalent: chainable styling
            +-- strutil.py      ANSI-aware string ops: width, wrap, truncate
            +-- layout.py       join_horizontal, join_vertical, place
            +-- components/
                    +-- textinput.py   Single-line input
                    +-- textarea.py    Multi-line editor
                    +-- viewport.py    Scrollable content
                    +-- list.py        Paginated list with delegates
                    +-- select.py      Option picker
                    +-- confirm.py     Yes/No prompt
                    +-- form.py        Multi-field form

In Go, these are spread across four repos (bubbletea, lipgloss, bubbles, x/ansi). snaptui combines them because Python apps can just import what they need from one package.

File mapping

Exact Go source → snaptui file mapping for reference when porting new features or chasing bugs back to the Go implementation.

Go source repos:

• bubbletea (v1.3.10) — event loop, renderer, key input
• lipgloss (v1.1.0) — styling, layout, borders
• bubbles (v1.0.0) — textinput, textarea, viewport, list
• huh (v0.8.0) — form, select, confirm, theme
• x/ansi (v0.11.6) — string width, wrap, truncate

snaptui file	Go source(s)
model.py	bubbletea/tea.go
program.py	bubbletea/tea.go, bubbletea/signals_unix.go
renderer.py	bubbletea/standard_renderer.go
keys.py	bubbletea/key.go, bubbletea/key_sequences.go
terminal.py	bubbletea/tty_unix.go, x/ansi/mode.go
style.py	lipgloss/style.go, lipgloss/set.go, lipgloss/get.go, lipgloss/color.go, lipgloss/borders.go, lipgloss/whitespace.go, lipgloss/size.go
layout.py	lipgloss/join.go, lipgloss/align.go, lipgloss/position.go
strutil.py	x/ansi/width.go, x/ansi/wrap.go, x/ansi/truncate.go, x/ansi/style.go
theme.py	huh/theme.go (Form theme); AppTheme/AppThemeCharm are snaptui-original
components/textinput.py	bubbles/textinput/textinput.go, bubbles/cursor/cursor.go
components/textarea.py	bubbles/textarea/textarea.go
components/viewport.py	bubbles/viewport/viewport.go, bubbles/viewport/keymap.go
components/list.py	bubbles/list/list.go, bubbles/list/defaultitem.go, bubbles/paginator/paginator.go
components/select.py	huh/field_select.go
components/confirm.py	huh/field_confirm.go
components/form.py	huh/form.go, huh/group.go

Running tests

python3 -m pytest