OpenAI API - GPT-4o for Production Applications

from openai import OpenAI
import json

client = OpenAI()  # reads OPENAI_API_KEY from env

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# 1. BASIC CHAT COMPLETION
# ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
response = client.chat.completions.create(
    model="gpt-4o",            # gpt-4o, gpt-4o-mini, o1, o1-mini
    messages=[
        {"role": "system", "content": "You are a Python expert."},
        {"role": "user", "content": "What is a generator in Python?"},
    ],
    temperature=0.7,            # 0=deterministic, 1=creative, 2=chaotic
    max_tokens=500,
    top_p=0.95,
    frequency_penalty=0.0,      # reduce repetition
    presence_penalty=0.0,       # encourage topic diversity
)

print(response.choices[0].message.content)
input_tokens  = response.usage.prompt_tokens
output_tokens = response.usage.completion_tokens
cost = input_tokens * 5e-6 + output_tokens * 15e-6  # gpt-4o pricing ($ per token)
print(f"Cost: ${cost:.5f}")

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# 2. STREAMING - real-time token output (like ChatGPT)
# ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
stream = client.chat.completions.create(
    model="gpt-4o-mini",
    messages=[{"role": "user", "content": "Write a haiku about AI."}],
    stream=True,               # tokens arrive incrementally
)
for chunk in stream:
    delta = chunk.choices[0].delta.content
    if delta:
        print(delta, end="", flush=True)
print()  # newline

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# 3. FUNCTION CALLING (Tool Use) - structured actions
# ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
# Model decides WHEN to call a function and with what arguments
# Your code executes the function - model never runs actual code

tools = [
    {
        "type": "function",
        "function": {
            "name": "get_weather",
            "description": "Get current weather for a city",
            "parameters": {
                "type": "object",
                "properties": {
                    "city": {"type": "string", "description": "City name"},
                    "units": {"type": "string", "enum": ["celsius", "fahrenheit"], "default": "celsius"},
                },
                "required": ["city"],
            },
        }
    }
]

response = client.chat.completions.create(
    model="gpt-4o",
    messages=[{"role": "user", "content": "What's the weather like in Tokyo right now?"}],
    tools=tools,
    tool_choice="auto",   # auto: model decides | "required": must call | "none": no tools
)

if response.choices[0].message.tool_calls:
    tool_call = response.choices[0].message.tool_calls[0]
    fn_name = tool_call.function.name           # "get_weather"
    fn_args = json.loads(tool_call.function.arguments)  # {"city": "Tokyo"}
    print(f"Tool call: {fn_name}({fn_args})")

    # Execute function (your code)
    weather_data = {"temp": 22, "condition": "sunny", "humidity": 55}

    # Return result to model
    follow_up = client.chat.completions.create(
        model="gpt-4o",
        messages=[
            {"role": "user", "content": "What's the weather in Tokyo?"},
            response.choices[0].message,  # assistant's tool call message
            {"role": "tool", "tool_call_id": tool_call.id, "content": json.dumps(weather_data)},
        ],
    )
    print(follow_up.choices[0].message.content)

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# 4. VISION - analyze images with GPT-4o
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vision_response = client.chat.completions.create(
    model="gpt-4o",
    messages=[{
        "role": "user",
        "content": [
            {"type": "text", "text": "Describe this image and identify any text visible."},
            {"type": "image_url", "image_url": {"url": "https://upload.wikimedia.org/wikipedia/commons/a/a7/Camponotus_flavomarginatus_ant.jpg"}},
        ]
    }],
    max_tokens=200,
)
print(vision_response.choices[0].message.content)