shiny-for-python

Shiny for Python

Shiny for Python (py-shiny) builds reactive web apps in pure Python. Two modes: Core (an explicit app_ui object plus a server(input, output, session) function) and Express (top-level code in the app file is the UI, with outputs defined inline). The reactive graph is the engine: reading a reactive source (input.x(), a reactive.value, a @reactive.calc) inside a reactive context registers a dependency, so changing that source re-runs everything that read it — you never call outputs or schedule updates yourself.

This skill is an index. Find your task below and read the linked reference file before writing code for that area.

Foundations

Topic	Use when	Reference
Reactivity	A value should recompute or an output update as inputs change; choosing between calc / effect / value; req, isolate, timers, polling, setting values from background tasks	references/reactivity.md
Express mode	Writing or converting an Express app (from shiny.express import ...); context-manager layout; page_opts, @expressify	references/express.md
Modules (Core)	A reusable, repeatable UI+server component in a Core app; avoiding input/output id collisions across copies	references/modules-core.md
Modules (Express)	The same reusable-component need in an Express app, via the single @module decorator	references/modules-express.md
Session lifecycle	Per-session cleanup (on_ended), reading request headers/cookies/URL, flush hooks, per-session routes	references/session-lifecycle.md

Dashboard building

Topic	Use when	Reference
Dashboard design	Turning a dataset or brief into a polished analytical dashboard; planning information hierarchy, shared filters, responsive layout, empty states, and the final visual/functional quality pass	references/dashboard-design.md
Dashboard components	Composing cards, KPI value boxes, local card toolbars, accessible icons, tooltips, and popovers	references/dashboard-components.md
Interactive charts	Rendering Plotly charts with shinywidgets; choosing chart forms, applying a coherent visual system, formatting hover/data labels, and handling empty data	references/interactive-charts.md
Maps	Choosing and rendering a geographic widget; cleaning coordinates, avoiding overplotting, and selecting Plotly, ipyleaflet, or lonboard by interaction and scale	references/maps.md

Layout & navigation

Topic	Use when	Reference
Layouts	Arranging a page into cards, columns, sidebars, value boxes, or accordions (bslib containers)	references/layouts.md
Navigation	Tabs, pills, or a navbar with multiple pages; reading/switching the active tab; runtime nav panels	references/navigation.md
Dynamic UI	UI that changes after render — @render.ui, ui.update_*, insert_ui/remove_ui, panel_conditional	references/dynamic-ui.md
Theming	Colors, fonts, Bootswatch presets, Sass variables, brand.yml, light/dark mode via ui.Theme	references/theming.md

Outputs & rendering

Topic	Use when	Reference
Static plots & images	Rendering matplotlib/seaborn/plotnine figures or images; static plot click/hover/brush interactions. For Plotly, read Interactive charts above	references/plots.md
Data frames	Interactive tables via @render.data_frame (DataGrid/DataTable) — sort, filter, select, edit	references/data-frames.md
Files	File uploads (ui.input_file) and generated-file downloads (@render.download_button/@render.download_link)	references/files.md

Feedback & interactivity

Topic	Use when	Reference
Feedback	Toasts/notifications, modal dialogs, progress bars, busy indicators	references/feedback.md
Extended tasks	Running slow work outside the session's reactive cycle so the session stays responsive; task buttons	references/extended-tasks.md
Bookmarking	Saving/restoring app state — shareable URLs, refresh persistence, server-side state	references/bookmarking.md

AI & streaming

Topic	Use when	Reference
Chat	Building an LLM chatbot with ui.Chat — streaming responses, wiring a provider, chat history	references/chat.md
Markdown streaming	Streaming Markdown/LLM text into a non-chat region with ui.MarkdownStream	references/markdown-streaming.md

Extending Shiny

Topic	Use when	Reference
Custom renderers	Authoring a reusable @render.xxx decorator by subclassing shiny.render.renderer.Renderer	references/custom-renderers.md
Custom components	Integrating custom browser JS — custom input/output bindings, send_custom_message, HTMLDependency assets	references/custom-components.md

Testing & observability

Topic	Use when	Reference
Test server	Testing server logic in memory with the local_server fixture / test_server() — set inputs, assert on outputs/exports, module scopes; no browser	references/test-server.md
Testing	End-to-end Playwright tests — launching an app under pytest, locating and asserting on UI	references/testing.md
Debugging	Inspecting server-side reactive/input/output state; exposing values to a test harness	references/debugging.md
OpenTelemetry	OTel tracing/profiling of reactive execution; exporting spans to a backend	references/otel.md