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The three Content modes

A Webview renders exactly one Content, declared as exactly one of three mutually exclusive modes.

from pathlib import Path

from dry import Webview

# An HTML string
Webview(html='<h1>Hello, World!</h1>')

# A URL
Webview(url='http://localhost:8000')

# A Root: a local directory, served starting at its index.html
Webview(root=Path(__file__).parent / 'dist')

There is no sniffing. Dry does not look at a string and decide whether it is markup, a path or an address; you say which it is, and the mode you named is the mode you get.

Declaring two, or none

Declaring a second mode raises as soon as you do it, naming the conflict and how to resolve it:

wv = Webview(html='<h1>Hi</h1>')
wv.url = 'https://example.com'
# ValueError: Content is already declared as html, so it cannot also be
# declared as url. A Webview renders exactly one of html, url or root.
# Set webview.html = None first.

Setting a mode back to None clears it, so switching is a two-step move on purpose:

wv.html = None
wv.url = 'https://example.com'

Declaring none is caught at run(), because a Webview may legitimately be built empty and filled in later:

Webview().run()
# ValueError: No content declared. A Webview renders exactly one of html, url
# or root: pass html=, url= or root= to Webview(...), or set the matching
# property before run().

html

An HTML string, loaded as the document. Anything relative inside it — <img src="logo.png">, <script src="./app.js"> — has no directory to resolve against, so html is for self-contained pages: markup, inline styles, inline scripts, and absolute URLs. The moment you have files beside your page, you want a Root.

url

Any address the platform’s web engine can load: a remote site, or a local server of your own. See Loading a URL from a local server.

root

A local directory served to the Webview over Dry’s own internal protocol, so relative assets resolve. This is the mode a compiled frontend wants — the output directory of a Vite, esbuild or Parcel build. See Serving a Root.

Content is fixed once the window opens

html, url and root are read while the Webview is being built. Assigning one after run() raises a RuntimeError naming the setting, rather than silently doing nothing. To change what the frontend shows while it is running, change it from the frontend — that is what wv.emit and wv.eval_js are for.