add context window exceeded error tutorial

docs/my-website/docs/tutorials/model_fallbacks.md

@@ -1,4 +1,4 @@
-# Basic Model Fallbacks w/ LiteLLM
+# Model Fallbacks w/ LiteLLM
 
 Here's how you can implement model fallbacks across 3 LLM providers (OpenAI, Anthropic, Azure) using LiteLLM. 
 
@@ -7,7 +7,7 @@ Here's how you can implement model fallbacks across 3 LLM providers (OpenAI, Ant
 !pip install litellm
 ```
 
-## 2. Complete Code 
+## 2. Basic Fallbacks Code 
 ```python 
 import litellm
 from litellm import embedding, completion
@@ -29,4 +29,32 @@ for model in model_fallback_list:
       response = completion(model=model, messages=messages)
   except Exception as e:
       print(f"error occurred: {traceback.format_exc()}")
+```
+
+## 3. Context Window Exceptions 
+LiteLLM provides a sub-class of the InvalidRequestError class for Context Window Exceeded errors ([docs](https://docs.litellm.ai/docs/exception_mapping)).
+
+Implement model fallbacks based on context window exceptions. 
+
+```python 
+import litellm
+from litellm import completion, ContextWindowExceededError, completion_with_fallbacks
+
+# set ENV variables
+os.environ["OPENAI_API_KEY"] = ""
+os.environ["ANTHROPIC_API_KEY"] = ""
+os.environ["AZURE_API_KEY"] = ""
+os.environ["AZURE_API_BASE"] = ""
+os.environ["AZURE_API_VERSION"] = ""
+
+context_window_fallback_list = ["gpt-3.5-turbo-16k", "gpt-4", "claude-instant-1"]
+
+user_message = "Hello, how are you?"
+messages = [{ "content": user_message,"role": "user"}]
+
+for model in context_window_fallback_list:
+  try:
+      response = completion(model=model, messages=messages)
+  except ContextWindowExceededError as e:
+      completion_with_fallbacks(model=context_window_fallback_list[0], messages=messages, fallbacks=context_window_fallback_list[1:])
 ```