How to build an AI agent: step by step, no-code or in Python, with GPT, Claude and DeepSeek

import json
from openai import OpenAI

client = OpenAI(base_url="https://www.ruapi.ai/v1", api_key="sk-...")

def get_weather(city):
    return f"It is +5 °C in {city} right now"  # your own code goes here

tools = [{
    "type": "function",
    "function": {
        "name": "get_weather",
        "description": "Weather in a city",
        "parameters": {
            "type": "object",
            "properties": {"city": {"type": "string"}},
            "required": ["city"],
        },
    },
}]

messages = [{"role": "user", "content": "What is the weather in Kazan?"}]
for _ in range(5):  # no more than 5 steps
    reply = client.chat.completions.create(
        model="deepseek-flash", messages=messages, tools=tools
    ).choices[0].message
    messages.append(reply)
    if not reply.tool_calls:  # the model answered in text — done
        print(reply.content)
        break
    for call in reply.tool_calls:  # the model asks to call a tool
        args = json.loads(call.function.arguments)
        messages.append({
            "role": "tool",
            "tool_call_id": call.id,
            "content": get_weather(**args),
        })
else:
    print("Step limit reached")