pyscript · WebReflection · Mar 2, 2026 · Mar 3, 2026 · Mar 3, 2026
diff --git a/README.md b/README.md
@@ -13,11 +13,11 @@ Using PyScript is as simple as:
         <title>PyScript!</title>
         <link
             rel="stylesheet"
-            href="https://pyscript.net/releases/2026.2.1/core.css"
+            href="https://pyscript.net/releases/2026.3.1/core.css"
         />
         <script
             type="module"
-            src="https://pyscript.net/releases/2026.2.1/core.js"
+            src="https://pyscript.net/releases/2026.3.1/core.js"
         ></script>
     </head>
     <body>

diff --git a/core/package-lock.json b/core/package-lock.json
diff --git a/core/package.json b/core/package.json
@@ -72,6 +72,7 @@
         "add-promise-listener": "^0.1.3",
         "basic-devtools": "^0.1.6",
         "polyscript": "^0.20.11",
+        "qsa-observer": "^3.0.2",
         "sticky-module": "^0.1.1",
         "to-json-callback": "^0.1.1",
         "type-checked-collections": "^0.1.7"

diff --git a/core/src/core.js b/core/src/core.js
@@ -3,6 +3,7 @@
 import "./zero-redirect.js";
 import stickyModule from "sticky-module";
 import withResolvers from "@webreflection/utils/with-resolvers";
+import QSAO from "qsa-observer";
 
 import {
     INVALID_CONTENT,
@@ -171,6 +172,7 @@ for (const [TYPE, interpreter] of TYPES) {
             PyWorker,
             fs,
             interpreter,
+            QSAO,
             js_import: (...urls) => Promise.all(urls.map((url) => import(url))),
             get target() {
                 return isScript(currentElement)

diff --git a/core/src/stdlib/pyscript.js b/core/src/stdlib/pyscript.js
diff --git a/core/src/stdlib/pyscript/events.py b/core/src/stdlib/pyscript/events.py
@@ -84,6 +84,30 @@ def remove_listener(self, *listeners):
             self._listeners = []
 
 
+from _pyscript import QSAO
+
+
+def handle(element, connected, selector):
+    for entries in Selectors[selector]:
+        (
+            event_type,
+            proxy,
+            options,
+        ) = entries
+        if connected:
+            element.addEventListener(
+                event_type, proxy, to_js(options) if options else False
+            )
+        else:
+            element.removeEventListener(event_type, proxy)
+
+
+Observed = to_js([])
+Selectors = {}
+
+QSAO = QSAO(to_js({"query": Observed, "handle": handle}))
+
+
 def when(event_type, selector=None, **options):
     """
     A decorator to handle DOM events or custom `Event` objects.
@@ -165,13 +189,27 @@ def decorator(func):
             for event in event_type:
                 event.add_listener(wrapper)
         else:
-            # DOM event - attach to all matched elements.
-            for element in elements:
-                element.addEventListener(
-                    event_type,
-                    create_proxy(wrapper),
-                    to_js(options) if options else False,
-                )
+            proxy = create_proxy(wrapper)
+
+            if "live" in options and options["live"]:
+                if selector not in Selectors:
+                    Selectors[selector] = []
+
+                Selectors[selector].append([event_type, proxy, options])
+
+                if not Observed.includes(selector):
+                    Observed.push(selector)
+                    QSAO.parse(elements)
+
+            else:
+                # DOM event - attach to all matched elements.
+                for element in elements:
+                    element.addEventListener(
+                        event_type,
+                        proxy,
+                        to_js(options) if options else False,
+                    )
+
         return wrapper
 
     return decorator

diff --git a/core/tests/manual/test_when.html b/core/tests/manual/test_when.html
@@ -11,14 +11,25 @@
         <p>Click for a hi!</p>
 
         <py-script>
-            from pyscript import window, when
-            @when("click", selector="#say-hi")
+            from pyscript import window, document, web, when
 
+            i = 0
+
+            @when("click", "#add-hi")
+            def add_hi():
+                global i
+                i += 1
+                button = web.button(f"Click Me {i}", classes=["say-hi"])
+                document.body.prepend(document.createElement("br"))
+                document.body.prepend(button._dom_element)
+
+            @when("click", selector=".say-hi", live=True)
             def say_hi(event):
                 window.alert("Hi! 🤗")
         </py-script>
 
-        <button id="say-hi">Click Me</button>
+        <button class="say-hi">Click Me</button>
+        <button id="add-hi">Add</button>
 
     </body>
 </html>