feat: Add ADK examples for litellm with add_function_to_prompt

Add examples for for https://github.com/google/adk-python/issues/1273

PiperOrigin-RevId: 775352677

contributing/samples/hello_world_litellm_add_function_to_prompt/__init__.py

@@ -0,0 +1,16 @@
+# Copyright 2025 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+
+from . import agent

contributing/samples/hello_world_litellm_add_function_to_prompt/agent.py

@@ -0,0 +1,78 @@
+# Copyright 2025 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+
+import random
+
+from google.adk import Agent
+from google.adk.models.lite_llm import LiteLlm
+from langchain_core.utils.function_calling import convert_to_openai_function
+
+
+def roll_die(sides: int) -> int:
+  """Roll a die and return the rolled result.
+
+  Args:
+    sides: The integer number of sides the die has.
+
+  Returns:
+    An integer of the result of rolling the die.
+  """
+  return random.randint(1, sides)
+
+
+def check_prime(number: int) -> str:
+  """Check if a given number is prime.
+
+  Args:
+    number: The input number to check.
+
+  Returns:
+    A str indicating the number is prime or not.
+  """
+  if number <= 1:
+    return f"{number} is not prime."
+  is_prime = True
+  for i in range(2, int(number**0.5) + 1):
+    if number % i == 0:
+      is_prime = False
+      break
+  if is_prime:
+    return f"{number} is prime."
+  else:
+    return f"{number} is not prime."
+
+
+root_agent = Agent(
+    model=LiteLlm(
+        model="vertex_ai/meta/llama-4-maverick-17b-128e-instruct-maas",
+        # If the model is not trained with functions and you would like to
+        # enable function calling, you can add functions to the models, and the
+        # functions will be added to the prompts during inferences.
+        functions=[
+            convert_to_openai_function(roll_die),
+            convert_to_openai_function(check_prime),
+        ],
+    ),
+    name="data_processing_agent",
+    description="""You are a helpful assistant.""",
+    instruction="""
+      You are a helpful assistant, and call tools optionally.
+      If call tools, the tool format should be in json, and the tool arguments should be parsed from users inputs.
+    """,
+    tools=[
+        roll_die,
+        check_prime,
+    ],
+)

contributing/samples/hello_world_litellm_add_function_to_prompt/main.py

@@ -0,0 +1,81 @@
+# Copyright 2025 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+
+import asyncio
+import time
+
+import agent
+from dotenv import load_dotenv
+from google.adk import Runner
+from google.adk.artifacts import InMemoryArtifactService
+from google.adk.cli.utils import logs
+from google.adk.sessions import InMemorySessionService
+from google.adk.sessions import Session
+from google.genai import types
+
+load_dotenv(override=True)
+logs.log_to_tmp_folder()
+
+
+async def main():
+  app_name = 'my_app'
+  user_id_1 = 'user1'
+  session_service = InMemorySessionService()
+  artifact_service = InMemoryArtifactService()
+  runner = Runner(
+      app_name=app_name,
+      agent=agent.root_agent,
+      artifact_service=artifact_service,
+      session_service=session_service,
+  )
+  session_11 = await session_service.create_session(
+      app_name=app_name, user_id=user_id_1
+  )
+
+  async def run_prompt(session: Session, new_message: str):
+    content = types.Content(
+        role='user', parts=[types.Part.from_text(text=new_message)]
+    )
+    print('** User says:', content.model_dump(exclude_none=True))
+    async for event in runner.run_async(
+        user_id=user_id_1,
+        session_id=session.id,
+        new_message=content,
+    ):
+      if event.content.parts:
+        part = event.content.parts[0]
+        if part.text:
+          print(f'** {event.author}: {part.text}')
+        if part.function_call:
+          print(f'** {event.author} calls tool: {part.function_call}')
+        if part.function_response:
+          print(
+              f'** {event.author} gets tool response: {part.function_response}'
+          )
+
+  start_time = time.time()
+  print('Start time:', start_time)
+  print('------------------------------------')
+  await run_prompt(session_11, 'Hi, introduce yourself.')
+  await run_prompt(session_11, 'Roll a die with 100 sides.')
+  await run_prompt(session_11, 'Check if it is prime.')
+  end_time = time.time()
+  print('------------------------------------')
+  print('End time:', end_time)
+  print('Total time:', end_time - start_time)
+
+
+if __name__ == '__main__':
+  asyncio.run(main())

src/google/adk/models/lite_llm.py

@@ -29,6 +29,7 @@ from typing import Tuple
 from typing import Union
 
 from google.genai import types
+import litellm
 from litellm import acompletion
 from litellm import ChatCompletionAssistantMessage
 from litellm import ChatCompletionAssistantToolCall
@@ -53,6 +54,9 @@ from .base_llm import BaseLlm
 from .llm_request import LlmRequest
 from .llm_response import LlmResponse
 
+# This will add functions to prompts if functions are provided.
+litellm.add_function_to_prompt = True
+
 logger = logging.getLogger("google_adk." + __name__)
 
 _NEW_LINE = "\n"
@@ -662,6 +666,10 @@ class LiteLlm(BaseLlm):
 
     messages, tools, response_format = _get_completion_inputs(llm_request)
 
+    if "functions" in self._additional_args:
+      # LiteLLM does not support both tools and functions together.
+      tools = None
+
     completion_args = {
         "model": self.model,
         "messages": messages,

tests/integration/models/test_litellm_with_function.py

@@ -17,11 +17,8 @@ from google.adk.models.lite_llm import LiteLlm
 from google.genai import types
 from google.genai.types import Content
 from google.genai.types import Part
-import litellm
 import pytest
 
-litellm.add_function_to_prompt = True
-
 _TEST_MODEL_NAME = "vertex_ai/meta/llama-3.1-405b-instruct-maas"
 
 _SYSTEM_PROMPT = """