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Version: 0.8

Recipe: Weather Agent

A complete, runnable agent that calls a real weather API as a tool. Demonstrates HTTP-calling tools, error handling, streaming UI, and cancellation.

Time to run: 5 minutes. Deps: cubepi, httpx, an ANTHROPIC_API_KEY.

The script​

weather_agent.py
import asyncio
import os

import httpx
from typing import Annotated
from pydantic import Field

from cubepi import Agent, AgentToolResult, TextContent, tool
from cubepi.providers.anthropic import AnthropicProvider


# --- The tool -----------------------------------------------------------

@tool
async def get_weather(
    city: Annotated[str, Field(description="The city to look up weather for")],
    units: Annotated[str, Field(pattern="^(metric|imperial)$")] = "metric",
) -> str | AgentToolResult:
    "Get current weather for a city. Returns a short text summary."
    # Free Open-Meteo geocoding + forecast.  No API key required.
    async with httpx.AsyncClient(timeout=10) as client:
        try:
            geo = await client.get(
                "https://geocoding-api.open-meteo.com/v1/search",
                params={"name": city, "count": 1, "language": "en"},
            )
            geo.raise_for_status()
            results = geo.json().get("results")
            if not results:
                # Returning is_error=True tells the model the call failed.
                return AgentToolResult(
                    content=[TextContent(text=f"Couldn't find a city named {city!r}.")],
                    is_error=True,
                )
            lat, lon = results[0]["latitude"], results[0]["longitude"]

            wx = await client.get(
                "https://api.open-meteo.com/v1/forecast",
                params={
                    "latitude": lat,
                    "longitude": lon,
                    "current_weather": True,
                    "temperature_unit": "celsius" if units == "metric" else "fahrenheit",
                },
            )
            wx.raise_for_status()
            cw = wx.json()["current_weather"]
            unit = "°C" if units == "metric" else "°F"
            # A plain str is wrapped as a successful text result.
            return f"{cw['temperature']}{unit}, wind {cw['windspeed']} km/h in {city}."
        except httpx.HTTPError as e:
            return AgentToolResult(
                content=[TextContent(text=f"Weather API error: {e}")],
                is_error=True,
            )


# --- The agent ----------------------------------------------------------

async def main():
    provider = AnthropicProvider(provider_id="anthropic", api_key=os.environ["ANTHROPIC_API_KEY"])
    agent = Agent(
        model=provider.model("claude-sonnet-4-6"),
        system_prompt="You are a concise weather assistant. Always use the tool; don't guess.",
        tools=[get_weather],
    )

    def on_event(event, signal=None):
        if event.type == "message_update" and event.stream_event.type == "text_delta":
            print(event.stream_event.delta, end="", flush=True)
        elif event.type == "tool_execution_start":
            print(f"\n[calling {event.tool_name}({event.args})]")
        elif event.type == "agent_end":
            print()

    agent.subscribe(on_event)

    # Wrap prompt() so Ctrl-C cleanly cancels the run.
    task = asyncio.create_task(agent.prompt("Weather in Tokyo and São Paulo, please."))
    try:
        await task
    except KeyboardInterrupt:
        agent.abort()
        await agent.wait_for_idle()


if __name__ == "__main__":
    asyncio.run(main())

Run:

pip install cubepi httpx
export ANTHROPIC_API_KEY=sk-…
python weather_agent.py

Sample output:

[calling get_weather({'city': 'Tokyo', 'units': 'metric'})]
[calling get_weather({'city': 'São Paulo', 'units': 'metric'})]
Tokyo is currently 18°C with a wind speed of 12 km/h. São Paulo is 25°C with winds of 9 km/h.

What's going on​

  • Two tools in parallel. The model emits two get_weather tool calls in the same assistant turn. CubePi runs them concurrently — the second one doesn't wait for the first.
  • Streaming text + tool events interleave. The on_event filter handles both text_delta (for the final answer) and tool_execution_start (for the "thinking" indicator).
  • Errors are tool results, not exceptions. A bad city or network hiccup returns is_error=True; the model gets the error message and usually retries with a different spelling.
  • Cancellation is clean. agent.abort() propagates through signal into in-flight tools and the provider stream.

Extending this recipe​

  • Add caching: memoize the geocoding lookup by city — Open-Meteo's coordinates are stable.
  • Add retries: wrap with RetryMiddleware to handle transient API errors.
  • Persist conversations: add a SQLiteCheckpointer so follow-up questions ("and in Osaka?") have history.

Run the example​

A self-contained, runnable version of this recipe is in the repository at examples/weather_agent.py.

git clone https://github.com/cubeplexai/cubepi && cd cubepi
uv sync

export ANTHROPIC_API_KEY=sk-ant-...   # or OPENAI_API_KEY [+ OPENAI_BASE_URL]
uv run --with httpx python examples/weather_agent.py

See also​