OpenAI's Chat Completion API adds function call functionality

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OpenAI has recently added a 'function calling' feature to its GTP API.

When you query an AI model in the OpenAI ChatAPI, you can provide an additional list of functions that the AI model can utilise to generate a response, When generating a response to a user's query, the AI model can select an appropriate function from the list of functions provided by the user and receive additional function responses from the user to generate the final response.

In other words, the existing AI model itself can be extended by providing additional information, or by automating the result of ChatGPT's response to take some action. For example, you can use it to

  • Generate a response from a user's request message that results from a web search (by calling a function).
  • Retrieve flight schedules from an airline site, suggest the cheapest flight, and take an action such as booking that flight.

This feature is supported by two newly released models: GPT-4-0613 and GPT-3.5-TURBO-0613.

How to use

If the user provides a list of function definitions in JSON format, the AI model can request a function call before responding to a user query. The function_call parameter controls whether the function is called or not.

  • auto - the AI model will automatically decide whether to call the function.
  • specific function name - requests that the AI model use that function
  • none - do not use

When the AI provides a response to a function call, the response is appended to the function_call property of the response message. When sending a Chat message to provide a response to a function, set the role to function and send it.

When using the Chat API with function calls, the process is as follows

  1. the user's query and functions provide a list of functions that the AI model can call. 2. the AI model calls the functions.
  2. the AI model decides whether to call the function.
  3. If the AI model uses the function, it returns a function call request response with the function name and call parameters to the user.
  4. When the user receives the function call response, call the function to generate the response.
  5. the user creates a new query by adding the function call response to the existing query and calls the CHAT API again.
  6. The AI model receives the new query and uses the function response to generate the final response.
graph TD style B fill:#f9f style C fill:#f9f style G fill:#f9f style H fill:#f9f A[User calls Chat API with a list of functions] --> B{{"AI model decides to use a function in the list for the query"}} B -->|Use a function| C["AI Model returns a function call request response with function name and call parameters"] B -->|Do not use a function| G[Generate the final response] C --> D[User calls a function] D --> E["Create a new query by adding the function call response value to an existing query"] E --> F[Call Chat API Again] F --> H["AI model takes the new query and utilises the function response to generate the final response"] G --> I[Return the final response] H --> I[Get the final response]

Below is an example of calling a function to get the weather provided by OpenAI. The print statement is added.

import openai
import json

# Example of a dummy function that always returns the same weather, in production it would be
# This could be code that calls a backend API or an external API.
def get_current_weather(location, unit="fahrenheit"):
    """Get the current weather in a given location"""
    weather_info = {
        "location": location,
        "temperature": "72",
        "unit": unit,
        "forecast": ["sunny", "windy"],
    return json.dumps(weather_info)

def run_conversation():
    # Step 1: Send a list of dialogues and available functions to GPT
    messages = [{"role": "user", "content": "What's the weather like in Boston?"}]
    functions = [
            "name": "get_current_weather",
            "description": "Get the current weather in a given location",
            "parameters": {
                "type": "object",
                "properties": {
                    "location": {
                        "type": "string",
                        "description": "The city and state, e.g. San Francisco, CA",
                    "unit": {"type": "string", "enum": ["celsius", "fahrenheit"]},
                "required": ["location"],
    response = openai.ChatCompletion.create(
        function_call="auto", # 'auto' is the default, but set for clarity
    response_message = response["choices"][0]["message"]

    # Step 2: Make sure GPT wants to call the function
    if response_message.get("function_call"):
        # Step 3: Call the function
        # Note: JSON responses may not always be valid, so be sure to handle errors.
        print("Function call response message:", response_message)
        available_functions = {
            "get_current_weather": get_current_weather,
        } # In this example, we only have one function, but you can have multiple.
        function_name = response_message["function_call"]["name"]
        fuction_to_call = available_functions[function_name]
        function_args = json.loads(response_message["function_call"]["arguments"])
        function_response = fuction_to_call(

        # Step 4: Add the response from the function call to the message and send it to GPT
        messages.append(response_message) # expand the dialogue of the GPT response
            { "role".
                "role": "function",
                "name": function_name,
                "content": function_response,
        ) # extend the dialogue with a function response
        second_response = openai.ChatCompletion.create(
        ) # Get a new response from GPT that confirms the added function response.
        return second_response

print("Final response: ", run_conversation())

Save the above example as and install and execute the openai library as shown below. Set the API key in the OPENAI_API_KEY environment variable and execute the example.

pip install openai


The result of the execution:

% python
함수 호출 응답 메세지: {
  "role": "assistant",
  "content": null,
  "function_call": {
    "name": "get_current_weather",
    "arguments": "{\n  \"location\": \"Boston\"\n}"
최종 응답:  {
  "id": "chatcmpl-7f2K8wMqviU1ALq9D2q81c28tVxin",
  "object": "chat.completion",
  "created": 1690014736,
  "model": "gpt-3.5-turbo-0613",
  "choices": [
      "index": 0,
      "message": {
        "role": "assistant",
        "content": "The current weather in Boston is sunny and windy with a temperature of 72 degrees."
      "finish_reason": "stop"
  "usage": {
    "prompt_tokens": 68,
    "completion_tokens": 17,
    "total_tokens": 85