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Dash — reactive dashboards

Version: 3.x
Type: Pure Python (+ bundled JS renderer assets)
SPM target: Dash
Auto-includes: Flask, Werkzeug, Jinja2, Markupsafe, Click, Plotly
Total Python modules: 211

Plotly-based dashboard framework — declarative layout (HTML + dcc components), reactive callbacks, interactive charts. Build a real on-device data app in a single Python file. Runs on Flask, served by Werkzeug; the JS renderer ships pre-built inside the package.

Modules

Core API (top-level)

Module What it does
dash.__init__ Public API exports: Dash, html, dcc, dash_table, Input, Output, State, MATCH, ALL, ALLSMALLER, ctx (callback context), no_update, Patch, clientside_callback, register_page
dash.dash The Dash application class
dash._callback @app.callback decorator — wires inputs/outputs to handlers
dash._callback_context ctx.triggered_id, ctx.inputs, ctx.states, ctx.outputs_grouping
dash._configs Config resolution (env vars, kwargs)
dash._dash_renderer Renderer asset wiring (the JS bundle for the browser)
dash._get_app / _get_paths App + path helpers used by pages and assets
dash._grouping Dict/list grouping helpers for nested outputs
dash._hooks Plugin / hook points
dash._jupyter Jupyter-mode integration
dash._no_update no_update sentinel for callbacks that conditionally skip outputs
dash._obsolete Friendly errors for renamed/removed APIs (e.g., app.run_server → app.run)
dash._pages Multi-page apps (register_page, automatic routing)
dash._patch Patch — partial updates to nested component props
dash._utils / _validate / _watch Internal helpers
dash.dependencies Input, Output, State, ClientsideFunction, MATCH/ALL/ALLSMALLER
dash.exceptions PreventUpdate, DuplicateCallback, NonExistentIdException, etc.
dash.fingerprint Asset-cache busting
dash.resources Resource (CSS/JS) registration
dash.types Type aliases
dash.version Package version
dash._plotly_cli Embedded plotly CLI shim

dash.html — HTML primitives (auto-generated)

One file per HTML element. Use any like html.Div(...), html.H1(...), etc.

Includes: Div, Span, H1–H6, P, A, Img, Button, Hr, Br, Pre, Code, Table, Thead, Tbody, Tr, Td, Th, Ul, Ol, Li, Form, Label, Input, Textarea, Select, Option, Header, Footer, Main, Section, Article, Aside, Nav, Figure, Figcaption, Details, Summary, Iframe, Canvas, Video, Audio, Source, Track, … (135+ tags).

dash.dcc — Dash Core Components

Interactive widgets. Auto-rendered by the JS renderer.

Component What it is
Graph Plotly figure renderer (the main charting widget)
Input Text / number / password input
Textarea Multi-line text
Dropdown Single + multi-select dropdown
Checklist Multi-check group
RadioItems Single-select radio group
Slider, RangeSlider Numeric sliders
DatePickerSingle, DatePickerRange Date pickers
Upload Drag-drop file upload
Markdown Render markdown (with mathjax, fenced code)
Tabs, Tab Tabbed layout
Store Client-side state
Interval Periodic timer (for live updates)
Loading Spinner wrapper for slow callbacks
Link, Location Client-side routing
Download Triggered file downloads
Clipboard Copy-to-clipboard
LogoutButton, ConfirmDialog, ConfirmDialogProvider Misc UX

dash.dash_table

Module What it does
dash_table.DataTable The interactive data grid: sort, filter, paginate, edit, dropdown cells, conditional formatting, row selection, virtualization, fixed headers

Plus Format / FormatTemplate helpers for column formatting.

dash.background_callback — long-running callbacks

Submodule Provides
background_callback.__init__ CeleryManager, DiskcacheManager
background_callback._proxy_set_props Async progress / set_progress hooks

iOS note: Celery + Diskcache backends aren't bundled by default. For dashboards that need long-running background work, use dcc.Loading + sync callbacks instead.

dash.development

Internal tools for component-library development (extracting metadata from React components). Not needed at runtime.

dash.testing

Selenium-based testing utilities. Doesn't apply on iOS — no Selenium.

iOS notes

Inherits all Flask + Werkzeug iOS patches (see werkzeug.md). Server starts via app.run() which calls flask.app.run() → werkzeug.serving.run_simple, so the preview-panel + clean-shutdown hooks fire automatically.

Dark-mode workaround: WKWebView auto-applies dark mode based on system preference. Dash's default-styled components render black-on-black. Override app.index_string to force a light color scheme — see web-stack.md § Dash for the snippet.

Feature test: dash_test.py — 6 tabs exercising every common component + callback pattern (including pattern-matching callbacks with ALL wildcard).

Example

import dash
from dash import Dash, html, dcc, Input, Output
import plotly.express as px
import pandas as pd

app = Dash(__name__)
app.layout = html.Div([
    html.H1("Live data"),
    dcc.Slider(id="n", min=10, max=200, step=10, value=50),
    dcc.Graph(id="chart"),
])

@app.callback(Output("chart", "figure"), Input("n", "value"))
def render(n):
    df = pd.DataFrame({"x": range(n), "y": [i*i for i in range(n)]})
    return px.line(df, x="x", y="y", title=f"y = x² for n={n}")

app.run(host="127.0.0.1", port=8050, debug=False)

See web-stack.md for the full iOS framework story.