Update handling of optional graphviz import

metricflow_semantics/dag/dag_visualization.py

@@ -2,9 +2,10 @@
 
 import logging
 import os
-from typing import TypeVar
+from typing import TYPE_CHECKING, TypeVar
 
-import graphviz
+if TYPE_CHECKING:
+    import graphviz
 from metricflow_semantics.dag.mf_dag import DagNode, MetricFlowDag
 from metricflow_semantics.toolkit.id_helpers import mf_random_id
 
@@ -42,7 +43,20 @@ def render_via_graphviz(dag_graph: DagGraphT, file_path_without_svg_suffix: str)
     Args:
         dag_graph: The DAG to render.
         file_path_without_svg_suffix: Path to the SVG file that should be created, without ".svg" suffix.
+
+    Raises:
+        RuntimeError: If the ``graphviz`` package is not installed.
     """
+    # `graphviz` is an optional dependency as rendering graphs is more of a debugging feature in tests / CLI.
+    # Since it's optional, import it locally only when needed.
+    try:
+        import graphviz
+    except ImportError as error:
+        raise RuntimeError(
+            "The `graphviz` Python package is required for DAG visualization."
+            " It can be installed with `pip install graphviz` or similar."
+            " Rendering may also require the `dot` executable from https://www.graphviz.org/ to be on your PATH."
+        ) from error
     dot = graphviz.Digraph(comment=dag_graph.dag_id, node_attr={"shape": "box", "fontname": "Courier"})
     # Not quite correct if there are shared nodes.
     for sink_node in dag_graph.sink_nodes: