Update app.py

app.py

@@ -4,6 +4,7 @@ import json
 import traceback
 from hardy_cross_solver import hardy_cross_solver
 from hardy_cross_plot import plot_hardy_cross_network
+import os
 
 def run_hardy_cross(file, loops_json, max_iterations, tolerance):
     try:
@@ -16,16 +17,26 @@ def run_hardy_cross(file, loops_json, max_iterations, tolerance):
             max_iterations=int(max_iterations),
             tolerance=float(tolerance)
         )
-        plot_path = "hardy_cross_network_result.png"
-        plot_hardy_cross_network(final_flows, save_path=plot_path)
+
+        # Generate and confirm plot path
+        plot_filename = "hardy_cross_network_result.png"
+        plot_path = plot_hardy_cross_network(final_flows, save_path=plot_filename)
+
+        # Double-check that the plot_path is a valid PNG file
+        if not (os.path.isfile(plot_path) and plot_path.endswith(".png")):
+            raise ValueError(f"Generated plot_path is invalid or not a PNG file: {plot_path}")
+
+        # Return structured outputs
         return (
             final_flows.to_markdown(),
             pd.DataFrame(results).to_markdown(),
             plot_path
         )
     except Exception as e:
-        # Capture full stack trace for clear debugging
-        error_message = f"Error: {str(e)}\n\nTraceback:\n{traceback.format_exc()}"
+        # Full traceback for clear debugging in output
+        error_message = f"❌ **Error:** {str(e)}\n\n```
+{traceback.format_exc()}
+```"
         return error_message, "", ""
 
 demo = gr.Interface(
@@ -46,4 +57,4 @@ demo = gr.Interface(
 )
 
 if __name__ == "__main__":
-    demo.launch()
+    demo.launch()