fix: widget.link() to support HoloViews streams

panel/reactive.py

@@ -800,7 +800,14 @@ def link_cb(*events):
                     if callbacks:
                         callbacks[event.name](target, event)
                     else:
-                        setattr(target, links[event.name], event.new)
+                        _is_hv_stream = (
+                            'holoviews' in sys.modules and
+                            isinstance(target, sys.modules['holoviews'].streams.Stream)
+                        )
+                        if _is_hv_stream:
+                            target.event(**{links[event.name]: event.new})
+                        else:
+                            setattr(target, links[event.name], event.new)
                 finally:
                     _updating.pop(_updating.index(event.name))
         params = list(callbacks) if callbacks else list(links)

panel/tests/test_reactive.py

@@ -59,6 +59,23 @@ class ReactiveLink(Reactive):
     assert obj2.a == 1
 
 
+def test_link_holoviews_stream():
+    "Link a Reactive object to a HoloViews stream"
+    try:
+        import holoviews as hv
+    except ImportError:
+        pytest.skip("holoviews not available")
+
+    class ReactiveLink(Reactive):
+        selection = param.List(default=[])
+
+    obj = ReactiveLink()
+    stream = hv.streams.Selection1D()
+    obj.link(stream, selection='index')
+    obj.selection = [0, 1]
+    assert stream.index == [0, 1]
+
+
 def test_param_rename():
     "Test that Reactive renames params and properties"