add langgraph use

examples/stream_modes/graph_visualize.py

@@ -0,0 +1,67 @@
+"""
+Demonstrate compiling a LangGraph and visualizing its structure.
+Requires no external viz packages for ASCII. To export PNG, install:
+  uv pip install -e '.[viz]'
+and ensure Graphviz is present on your system.
+"""
+
+from typing import TypedDict, Annotated
+import operator
+
+from langgraph.graph import StateGraph, START, END
+
+
+class S(TypedDict):
+    a: int
+    b: int
+    c: int
+
+
+def n1(s: S) -> S:
+    return {"a": s.get("a", 0) + 1, "b": s.get("b", 0), "c": s.get("c", 0)}
+
+
+def n2(s: S) -> S:
+    return {"a": s.get("a", 0), "b": s.get("b", 0) + 2, "c": s.get("c", 0)}
+
+
+def n3(s: S) -> S:
+    return {"a": s.get("a", 0), "b": s.get("b", 0), "c": s.get("c", 0) + 3}
+
+
+def build_app():
+    g = StateGraph(S)
+    g.add_node("n1", n1)
+    g.add_node("n2", n2)
+    g.add_node("n3", n3)
+    g.add_edge(START, "n1")
+    g.add_edge("n1", "n2")
+    g.add_edge("n2", "n3")
+    g.add_edge("n3", END)
+    return g.compile()
+
+
+def main():
+    app = build_app()
+    graph = app.get_graph()
+
+    # Try ASCII render if available
+    draw_ascii = getattr(graph, "draw_ascii", None)
+    if callable(draw_ascii):
+        print("=== Graph ASCII ===")
+        print(draw_ascii())
+
+    # Try PNG export if available and pydot/graphviz installed
+    draw_png = getattr(graph, "draw_png", None)
+    if callable(draw_png):
+        try:
+            out = "graph_demo.png"
+            draw_png(out)
+            print(f"Saved PNG: {out}")
+        except Exception as e:
+            print(f"PNG export unavailable: {e}")
+
+
+if __name__ == "__main__":
+    main()
+