Fix NameError when pydot is not installed in Beam Playground (#38074)

liferoad · web-flow · commit 46052504435e · 2026-04-08T19:49:51.000-04:00
When pydot is not installed, the import in pipeline_graph.py fails silently (caught by 'except ImportError: pass'), and subsequent calls to pydot.Dot() raise a confusing NameError with no context. Now _construct_graph() checks if pydot is available before use and raises a clear RuntimeError with install instructions instead. Fixes #37829
diff --git a/sdks/python/apache_beam/runners/interactive/display/pipeline_graph.py b/sdks/python/apache_beam/runners/interactive/display/pipeline_graph.py
@@ -237,6 +237,12 @@ def _construct_graph(
       default_edge_attrs: (Dict[str, str]) a dict of attributes
     """
     with self._lock:
+      try:
+        pydot.Dot()
+      except NameError:
+        raise RuntimeError(
+            'pydot is required for pipeline graph generation. '
+            'Install it with: pip install pydot')
       self._graph = pydot.Dot()
 
       if default_vertex_attrs:
