move get_fallback_model and fallback_model to the beginning

app.py

@@ -234,16 +234,25 @@ def initialize_model_once(model_key):
         
     return MODEL_CACHE["tokenizer"], MODEL_CACHE["model"], MODEL_CACHE.get("is_gguf", False)
 
+def get_fallback_model(current_model):
+    """Get appropriate fallback model for problematic models"""
+    fallback_map = {
+        "Phi-4 Mini Instruct": "TinyLlama Chat",
+        "DeepSeek Lite Chat": "DeepSeek Coder Instruct",
+        "Flan T5 Small": "Llama 2 Chat"
+    }
+    return fallback_map.get(current_model, "Llama 2 Chat")
+
 def create_llm_pipeline(model_key):
     """Create a new pipeline using the specified model with better error handling"""
     try:
         print(f"Creating pipeline for model: {model_key}")
+        fallback_model = get_fallback_model(model_key)  # Define fallback_model at the beginning
         tokenizer, model, is_gguf = initialize_model_once(model_key)
 
         # Additional check to ensure model was properly loaded
         if model is None:
             print(f"Model is None for {model_key}, falling back to alternate model")
-            fallback_model = get_fallback_model(model_key)
             if fallback_model != model_key:
                 print(f"Attempting to use fallback model: {fallback_model}")
                 tokenizer, model, is_gguf = initialize_model_once(fallback_model)
@@ -303,15 +312,6 @@ def create_llm_pipeline(model_key):
         print(traceback.format_exc())
         raise RuntimeError(f"Failed to create pipeline: {str(e)}")
 
-def get_fallback_model(current_model):
-    """Get appropriate fallback model for problematic models"""
-    fallback_map = {
-        "Phi-4 Mini Instruct": "TinyLlama Chat",
-        "DeepSeek Lite Chat": "DeepSeek Coder Instruct",
-        "Flan T5 Small": "Llama 2 Chat"
-    }
-    return fallback_map.get(current_model, "TinyLlama Chat")
-
 # Modified handle_model_loading_error function
 def handle_model_loading_error(model_key, session_id):
     """Handle model loading errors by providing alternative model suggestions or fallbacks"""