Raise a clear type error for unsupported Perspective objects (#8720)

Author: ghostiee-11

panel/pane/perspective.py

@@ -363,6 +363,11 @@ def __init__(self, object=None, **params):
     def _get_data(self):
         if self.object is None:
             return {}, {}
+        # ReactiveData builds the data during super().__init__, before PaneBase
+        # gets to validate the object, so the type check has to happen here to
+        # cover both construction and later assignment to .object.
+        if self.applies(self.object) is False:
+            self._type_error(self.object)
         if isinstance(self.object, dict):
             ncols = len(self.object)
             df = data = self.object

panel/tests/pane/test_perspective.py

@@ -1,3 +1,5 @@
+import pytest
+
 from panel.pane import Perspective
 
 data = {
@@ -10,6 +12,18 @@
  }
 
 
+def test_perspective_rejects_unsupported_object():
+    with pytest.raises(ValueError, match='does not support objects of type'):
+        Perspective('not tabular')
+
+
+def test_perspective_rejects_unsupported_object_on_assignment():
+    psp = Perspective(data)
+
+    with pytest.raises(ValueError, match='does not support objects of type'):
+        psp.object = 'not tabular'
+
+
 def test_perspective_int_cols(document, comm):
     psp = Perspective(
         data, columns=[0], aggregates={0: 'mean'}, sort=[[0, 'desc']],