nextpytk

Accessible, declarative Tkinter applications from ordinary Python functions.

Register widgets as plain Python functions, declare layout separately, and keep roles/descriptions in one place. The decorator style is Flask-inspired; schema() exports the registered widget structure as JSON-compatible data. Uses ttk widgets where available.

Quick Start

Start with an app where a button updates a message.

pip install nextpytk

from nextpytk import TkApp

app = TkApp(title="Hello")

@app.status("msg")
def msg():
    return "Hello, world!"

@app.button("greet", label="Greet")
def on_greet():
    return {"msg": "Button clicked!"}

app.run(layout=["msg", "greet"])

How it works

In nextpytk you register widgets by name and declare layout separately.

This example registers two widgets: msg and greet.

@app.status("msg")

msg is a status area that shows a message.

@app.button("greet", label="Greet")

greet is a button labeled "Greet".

Finally, name the display order:

app.run(layout=["msg", "greet"])

When you press the button, the callback returns this dict:

{"msg": "Button clicked!"}

nextpytk merges that into the app state.

Because msg is the name of the registered status area, its text becomes "Button clicked!".

So the basic flow is:

• Register widgets by name
• List those names in the layout
• Return a dict from a callback
• state updates and matching widgets refresh

Using input values

Next, change the app so you type a name and press Greet.

from nextpytk import TkApp

app = TkApp(title="Hello")

@app.entry("name", placeholder="Name")
def on_name():
    return {}

@app.status("msg")
def msg():
    return "Enter your name"

@app.button("greet", label="Greet")
def on_greet(values):
    name = values["name"]
    return {"msg": f"Hello, {name}!"}

app.run(layout=["name", "greet", "msg"])

entry registers a text field.

@app.entry("name", placeholder="Name")

Again, "name" is the widget name. An on-change callback is required; if you only read the field from a button, a no-arg callback that returns {} is enough.

In the button callback, read the current field value from values:

def on_greet(values):
    name = values["name"]

values["name"] is the current value of the entry registered as name.

For example, if you type

Taro

and press the button, the callback returns:

{"msg": "Hello, Taro!"}

That dict merges into state and updates the status area named msg.

values and state

Two dictionaries appear here:

• values Input values at the moment the callback runs

• state Shared current state for the whole app

A button callback reads values, then returns a dict of state changes:

def on_greet(values):
    name = values["name"]
    return {"msg": f"Hello, {name}!"}

The flow is:

• Type into an entry
• Press the button
• Read input from values
• Return updates as a dict
• Those updates merge into state
• Matching widgets refresh from state

That is nextpytk's basic state-update model.

Design System

nextpytk ships with typed constants and design tokens. Prefer them over raw tkinter strings and magic numbers so every app stays consistent and IDE completion works out of the box.

Typed Constants

from nextpytk.types import Side, Fill, Sticky, State, Orient

Layout().section("msg", side=Side.LEFT, fill=Fill.X)

Each type has a matching *Like literal alias (e.g. FillLike), so raw strings still work when needed.

Event sequences

Use EventSeq constants for widget-level event bindings (events= on @app.listbox and @app.entry). These handlers are separate from the widget's select/change callback:

from nextpytk.types import EventSeq, SelectMode

@app.listbox(
    "results",
    items_key="results_items",
    selectmode=SelectMode.BROWSE,
    events={
        EventSeq.RETURN: lambda state: open_child(),
        EventSeq.PRIMARY_DOUBLE_CLICK: lambda state: open_child(),
        EventSeq.BACKSPACE: lambda state: go_parent(),
    },
)
def on_results_select(idx: int) -> dict:
    return {"status": f"selected:{idx}"}

@app.entry(
    "query",
    events={
        EventSeq.RETURN: lambda values: {
            "status": f"search:{(values.get('query') or '').strip()}"
        },
    },
)
def on_query(value: str) -> dict:
    return {}

EventSeq.PRIMARY_CLICK, EventSeq.PRIMARY_DOUBLE_CLICK, and EventSeq.PRIMARY_BUTTON_RELEASE are a11y-aware lazy descriptors that return the event sequence for the OS-configured primary mouse button (accounting for left/right button swap on Windows, macOS, and Linux/GNOME).

Dynamic choices

State-driven choices mirror treeview's rows_key: keep the selection in state[name] / state[key], and refresh the options via a separate key.

@app.listbox("results", items_key="results_items")
def on_results_select(idx: int) -> dict:
    return {}

@app.combobox("folder", values_key="folder_values")
def on_folder(value: str) -> dict:
    return {}

# Later (button, job, or initial_state):
app.apply_state({
    "results_items": ["a", "b", "c"],
    "folder_values": ["INBOX", "Sent"],
})

Omit items_key / values_key to keep a static items= / values= list.

Spacing tokens

from nextpytk.tokens import SPACE

SPACE[1]  # 4px  — small padding inside a widget
SPACE[2]  # 8px  — adjacent widgets
SPACE[3]  # 12px — section inner gaps
SPACE[4]  # 16px — section margins
SPACE[6]  # 24px — large blocks
SPACE[8]  # 32px — page-level gaps

The scale is based on a 4px unit and only common steps are provided. Use SPACE[n] for every padx/pady value and for widget-level padding values where practical.

Themes

TkApp accepts a theme parameter:

# Use the platform default ttk theme
app = TkApp(title="Native", theme="none")

# Use any installed ttk theme
app = TkApp(title="Clam", theme="clam")

See examples/header_demo.py for Layout.header() / .status() chrome and nextpytk.theme.apply_theme() usage.

Multiview (Multi-tab)

from nextpytk import TkApp, Layout

app = TkApp(title="Multi-tab App")

@app.status("header")
def header(): return "Common header"

with app.view("Tab1", layout=Layout().section("t1_label", "t1_btn")) as v:
    @v.label("t1_label")
    def t1_label(): return "Tab 1 content"
    @v.button("t1_btn", label="Click")
    def t1_btn(vals): return {}

with app.view("Tab2", layout=Layout().section("t2_label")) as v:
    @v.label("t2_label")
    def t2_label(): return "Tab 2 content"

@app.multiview(
    "main",
    views=["Tab1", "Tab2"],
    toplevel_widgets=("header",),
    initial_state={"tab": "Tab1"},
    on_tab_change=lambda tab: {"tab": tab},
)
def main_multiview(): pass

app.run(multiview="main")

View layouts also accept lists or with-block builders. For example, view_layouts values may be simple widget-name lists:

view_layouts = {
    "Home": ["title", "start"],
    "Settings": ["timer", "status"],
}

Layout DSL

Three styles — pick the one that fits:

from nextpytk import Layout

# 1) Simple list (easiest)
app.run(layout=["msg", "greet"])

# 2) Fluent DSL
app.run(layout=Layout().section("msg").section("greet"))

# 3) with-block (context manager)
with app.layout() as b:
    b.section("msg")
    b.section("greet")
app.run(layout=b.build())

Simple list

app.run(layout=["title", "timer", "start", "status"])

Each name gets its own pack-based section. Extra kwargs forwarded to section():

Layout.from_list(["a", "b"], fill="both", expand=True)

Layout spacing

The default block padding comes from the design token SPACE[1] (4 px). Pass spacing=... to a Layout constructor to change the default padding for every block it creates:

from nextpytk import tokens

layout = Layout(spacing=2).section("a").section("b").grid().widget("c").end_grid()

spacing accepts a key from nextpytk.tokens.SPACE (1, 2, 3, 4, 6, 8). It sets the default padx and pady used by section(), grid(), paned(), grid widget() placements, and nested frames. Explicit padx/pady arguments still override the default.

For finer control, pass padx or pady directly to the constructor:

Layout(padx=tokens.SPACE[4], pady=tokens.SPACE[3]).section("a")

Nested frames

A Layout can be placed inside a named frame to group widgets visually without mixing pack and grid in the same parent. The inner layout owns its own spacing and may use any layout style (pack sections, grid, paned, or further nested frames).

inner = Layout().section("a", "b")
outer = Layout().section("title").frame("group", inner).section("ok")
app.run(layout=outer)

frame(name, layout, side=..., fill=..., expand=..., padx=..., pady=...) packs the inner layout as a single block. The frame itself is registered under name, so it can also be placed inside a grid cell:

outer = (
    Layout()
    .grid()
    .widget("label")
    .widget("group", sticky="nsew")
    .end_grid()
    .frame("group", Layout().section("a", "b"))
)

Paired layout

Layout.paired(left, right, ...) places two widgets side by side in a single two-column frame. It is a lighter alternative to app.paned for diff/compare views:

layout = (
    Layout()
    .section("info")
    .paired(
        "left_text",
        "right_text",
        weight=(1, 1),
        fill=Fill.BOTH,
        expand=True,
        sync_yscroll=True,
    )
)

Options:

When sync_yscroll=True and both widgets are @app.text widgets, scrolling either pane moves the other. For text widgets the same effect can also be achieved per-widget with @app.text(..., sync_yscroll_with="other"); paired layout provides a layout-level switch that works without editing widget declarations.

With line_numbers=True each side gains a read-only line-number gutter. Both panes and both gutters share a single vertical scrollbar, so the gutters stay in lock-step with the content (no drift). Logical line numbers (1..n) follow the pane content; the right pane's numbers update as you edit.

Note: line_numbers=True takes precedence over sync_yscroll. The shared-scrollbar layout it installs keeps both panes (and both gutters) scrolled in lock-step, so passing sync_yscroll=False together with line_numbers=True has no effect. If the panes must scroll independently, leave line_numbers off.

Wrap layout

Layout.wrap() is a wrapping flow (Flutter Wrap analog): widgets are not stretched to fill a column; each keeps the width implied by its content or width= and they lay out left to right, wrapping to the next row whenever the next widget no longer fits in the remaining frame width. Widgets in the same row are vertically centered on their midline, so a tall entry aligns cleanly with a shorter button or checkbutton. The gap inherits the layout spacing by default (gapx/gapy override it independently).

TAGS = ["python", "tkinter", "async", "uv", "type hints"]
for tag in TAGS:
    @app.button(tag, label=f"#{tag}")
    def on_tag(values, tag=tag):
        return {"msg": f"Selected: {tag}"}

app.run(layout=Layout(spacing=2).status("msg").wrap(*TAGS))

Wrap is ideal for tag clouds, toolbars, and filter UIs. The layout recomputes rows automatically when the window is resized. Pass gapx/gapy to override the spacing default, and side/fill/expand to control how the wrap frame is packed.

Any wrap child wrapped in Flex(name, flex=...) absorbs leftover horizontal space in its row (Flutter Expanded analog):

from nextpytk import Flex

app.run(layout=Layout().wrap("filter", Flex("search", flex=2), "ok", gapx=2))

For custom positioning, Layout.flow() takes a FlowDelegate (Flutter Flow analog) that computes each child's (x, y, width, height) from the available Constraints. See examples/wrap_demo.py for both Flex and Flow usage.

How it works. wrap and flow position children with place (absolute x/y) because pack cannot reflow onto new rows — with pack -side left an overflowing child simply falls off the edge. place therefore implies a few constraints:

• All children share one parent frame and are place-managed; they cannot also be pack/grid-managed on the same master (mixing geometry managers raises TclError: conflicting geometry managers).
• Widths come from winfo_reqwidth(); the frame uses pack_propagate(False) and its height is explicit.
• On resize the flow is recomputed so rows re-wrap to the new width.

Because place bypasses Tk's native Tab traversal (which follows pack/grid insertion order), wrap intercepts <Tab>/<Shift-Tab> and moves focus in the visual row-major order instead. Entry/Text children are skipped (Tab stays for text input); focus wraps between the first and last wrap item.

Note: Layout.cluster() was renamed to Layout.wrap() in 0.5.0. cluster() remains as a deprecated alias and will be removed in 0.5.0.

Dynamic region switching (swap targets)

Layout.target() reserves a region whose contents change at runtime, mirroring HTMX hx-target / hx-swap. Surrounding sections (toolbar, status) stay fixed while only the target region swaps:

layout = Layout().wrap("go_dir", "go_file", "info").target("main_area")

@app.swap(
    "main_area",
    variants={
        "dir":  [Layout().section("dir_tree")],
        "file": [Layout().paired("left_text", "right_text",
                                 fill=Fill.BOTH, expand=True)],
    },
    default="dir",
)
def main_area():
    pass

# Switch imperatively at runtime:
app.swap_view("main_area", "file")

@app.swap variants are mounted up-front and shown/hidden via pack, so widget state (e.g. a treeview selection or scroll position) survives switching. Each variant is a Layout or a list of widget names. See examples/swap_demo.py.

Fluent DSL

Pack sections:

Layout().section("msg").section("phase", "count").section("start", "pause")

Grid builder:

from nextpytk.types import Sticky

layout = (
    Layout()
    .grid()
    .span(2).widget("title", sticky=Sticky.W)
    .next_row()
    .widget("label", sticky=Sticky.RIGHT).widget("input", sticky=Sticky.LEFT_RIGHT)
    .next_row()
    .span(2).widget("ok")
    .end_grid()
)

Grid builder methods:

Use col_weight(0, 0).col_weight(1, 1) to set column 0 → weight 0 and column 1 → weight 1.

With-block (context manager)

from nextpytk import LayoutBuilder

# Standalone builder
builder = LayoutBuilder()
with builder:
    builder.section("title")
    with builder.grid():
        builder.col_weight(0, 0).col_weight(1, 1)
        builder.widget("celsius", sticky="ew")
        builder.widget("fahrenheit", sticky="ew")
        builder.next_row().span(2).widget("note")
app.run(layout=builder.build())

# Via app.layout() shortcut
with app.layout() as b:
    b.section("title")
    with b.grid():
        b.col_weight(0, 0).col_weight(1, 1)
        b.widget("celsius", sticky="ew")
app.run(layout=b.build())

with b.grid(...) auto-closes — no end_grid() needed.

grid() options available directly: padx, pady, fill, expand, uniform.

Widget Reference

@app.status sets schema / accessible role="status" metadata. It is not an ARIA live region yet (planned for a later release). Prefer it for operation feedback labels; use @app.label for static or high-frequency mirror text.

File picker

@app.filepicker creates a button that opens a tkinter file dialog. The selected path(s) are passed to the callback; None on cancel.

@app.filepicker("open_file", mode="open", label="Open file",
                title="Open file", filetypes=[("Text files", "*.txt")])
def pick_open_file(path: str | None) -> dict[str, Any]:
    return {"open_path": path}

Modes: "open" (default), "open_multiple", "save", "directory".

A filepicker can also be invoked from a menubar item by using its name as the command:

@app.filepicker("m_open", mode="open", title="Open file")
def m_open(path):
    return {"open_path": path}

@app.menubar("menu")
def menu_bar():
    return [{"label": "File", "items": [
        {"label": "Open...", "command": "m_open"},
    ]}]

app.run(stages=..., tabposition=...) and @app.stages provide state-driven screen switching (one visible stage at a time). Theme helpers (apply_theme, tokens, layout chrome) ship in the package root — see examples/header_demo.py.

Common options:

• font: (family, size[, weight]) tuple, e.g. font=("TkDefaultFont", 18, "bold")
• padding: internal padding; integer or (x, y) / (left, top, right, bottom) tuple, e.g. padding=4 or padding=(4, 2)

Label options: font, anchor, justify, padding, width.

Entry options: placeholder, show, font, padding, width, state.

• padding is the declarative way to increase visual height (ttk.Entry does not support height).

Button, checkbutton, radiobutton, spinbox, combobox, listbox, text options:

• font is accepted uniformly. Under the hood, ttk widgets use a derived style so the rest of the theme (colors, maps, layout) is inherited.

Text options (continued):

• wrap: Wrap.WORD (default) / Wrap.NONE / Wrap.CHAR. Wrap.NONE keeps each logical line on a single row.
• h_scroll: when True, a horizontal scrollbar is added (and wired to xscrollcommand) so long lines are reachable, typically used with wrap=Wrap.NONE.

Every widget decorator also accepts widget_kwargs: dict for per-widget design-token overrides applied after construction. Keys are widget-native tk/ttk options (padx, pady, bg, fg, font, …). An invalid/unknown key is ignored rather than aborting the build:

@app.text("log", wrap="none", h_scroll=True,
          widget_kwargs={"bg": "#1e1e1e", "fg": "#dcdcdc"})
def log(value): return {}

Runtime access: app.text_widget(name) returns the real tk.Text; app.layout_frame(name) returns the layout section frame that owns a widget (for manual grid/pack placement or re-parenting). app.on_text_set(name, hook) registers a callback to run after a text widget's content is replaced (used by paired line-number gutters).

Enum-like options (wrap, state, orient, selectmode, mode) are validated at registration time: an invalid value raises a clear ValueError naming the option and the allowed values, instead of failing later with a TclError when the widget is built.

@app.message creates an auto-wrapping label. width sets initial pixel width; auto_width=True (default) tracks parent container resize.

Typed Constants

from nextpytk.types import Side, Fill, Sticky, State, Orient

Layout().section("msg", side=Side.LEFT, fill=Fill.X)

Values use str literals compatible with tkinter. SideLike / FillLike etc. accept raw strings too.

Schema Export

app.schema() returns a JSON-compatible snapshot of registered widgets (name, kind, label, role, description, plus kind-specific fields).

@app.label("temperature")
def t():
    return "25°C"

app.schema()
# → {"title": "...", "widgets": [{"name": "temperature", "kind": "label", ...}]}

Layout debug

After widgets are built, app.debug_layout() returns JSON-compatible geometry and pack/grid info for every registered widget (useful for clipping, minsize, and layout regressions).

app.run(layout=["msg", "go"])  # or build via tests / custom runner
print(app.debug_layout())
# → {"title": "...", "sections": [{"widgets": [{"name": "msg", "geometry": ..., ...}, ...]}]}

Detecting geometry-manager conflicts. Mixing pack/grid/place on one master (e.g. manually pack/grid-ing into a place-managed wrap/flow frame) cannot be fully prevented by the DSL, so app.check_layout_conflicts() inspects the widget tree and reports any such mix without waiting for a TclError: conflicting geometry managers:

print(app.check_layout_conflicts())
# → [{"master_class": "Frame", "managers": ["pack", "place"], ...}] on conflict
#    (a warning is also emitted for each conflict)

Async-Native (asyncio + Tkinter)

app.run_async() runs the app on an asyncio event loop, cooperatively scheduled with the Tk main loop via root.tk.dooneevent(0). app.spawn(coro) schedules async tasks during GUI runtime. @app.job(name) registers async callables.

@app.job("scan")
async def scan(vals):
    result = await asyncio.to_thread(some_blocking_call)
    return {"status": "done"}

app.run_async(layout=Layout().section("status"))

Examples

uv run python examples/grid_temp.py          # temperature converter
uv run python examples/task_panel.py          # multi-button panel
uv run python examples/multiscreen.py         # order app with screens
uv run python examples/widget_gallery.py      # all widget types
uv run python examples/header_demo.py         # Layout.header / .status chrome
uv run python examples/combobox_demo.py       # ttk.Combobox
uv run python examples/menubar_demo.py        # menubar
uv run python examples/filepicker_demo.py     # file picker
uv run python examples/disk_usage_flat_async.py       # ncdu-style viewer (async)
uv run python examples/paired_demo.py           # side-by-side paired layout with y-scroll sync
uv run python examples/swap_demo.py             # dynamic region switching (Layout.target + @app.swap)
uv run python examples/bottom_bar_demo.py       # pinned bottom bar (section side="bottom")

Requirements

• Python 3.13+ (requires-python; examples default to 3.14 via Makefile PYTHON=...)
• Tkinter support in your Python build
• No other dependencies

Note: On some macOS environments, uv + 3.14+freethreaded can fail at Tk startup with Can't find a usable init.tcl. You can switch runtimes per command, e.g. make run PYTHON=3.13, make run PYTHON=3.14+freethreaded, make run PYTHON=3.15.

Related Projects

• tkinter (stdlib): nextpytk builds on top — adding Decorator / Schema / A11y layers.
• ttk: Native look and accessibility; nextpytk prefers ttk widgets where available.
• CustomTkinter: Modern look via Canvas rendering. nextpytk takes the opposite approach: use native widgets and embed A11y from the start.
• TkRouter (israel-dryer, author of ttkbootstrap): Declarative view routing with URL-style paths, animated transitions, and history stack. Complements nextpytk's multiview — routing vs widget composition.

License

MIT

Author

Takuya Nishimoto — Shuaruta Inc.