Weather lookup

Instructions

Implementation Reference

• nanomcp/server.py:151-167 (handler)

  The main handler function for the 'get_weather' tool. Takes location and optional unit arguments, dispatches to live_weather (if NANOMCP_LIVE_WEATHER=1) or offline_weather (deterministic demo data).

  def get_weather(arguments: dict[str, Any]) -> str:
      location = str(arguments.get("location", "")).strip()
      if not location:
          raise ToolError("location is required")
  
      unit = str(arguments.get("unit", "celsius"))
      if unit not in {"celsius", "fahrenheit"}:
          raise ToolError("unit must be celsius or fahrenheit")
  
      if os.environ.get("NANOMCP_LIVE_WEATHER") == "1":
          try:
              return live_weather(location, unit)
          except Exception as exc:
              offline = offline_weather(location, unit)
              return f"Live weather lookup failed ({exc}).\n\n{offline}"
  
      return offline_weather(location, unit)

• nanomcp/server.py:23-48 (schema)

  Tool schema definition for 'get_weather' in the TOOLS list, specifying inputSchema with location (required string) and unit (optional enum: celsius/fahrenheit).

  TOOLS: list[dict[str, Any]] = [
      {
          "name": "get_weather",
          "title": "Weather lookup",
          "description": (
              "Get current weather for a city. By default this returns deterministic "
              "demo data. Set NANOMCP_LIVE_WEATHER=1 to try wttr.in."
          ),
          "inputSchema": {
              "type": "object",
              "properties": {
                  "location": {
                      "type": "string",
                      "description": "City or place name, for example Shanghai.",
                  },
                  "unit": {
                      "type": "string",
                      "enum": ["celsius", "fahrenheit"],
                      "description": "Temperature unit.",
                      "default": "celsius",
                  },
              },
              "required": ["location"],
              "additionalProperties": False,
          },
      },

• nanomcp/server.py:136-139 (registration)

  Registration/dispatch point in call_tool() that routes the 'get_weather' tool name to the get_weather() handler function.

  def call_tool(name: str, arguments: dict[str, Any]) -> dict[str, Any]:
      try:
          if name == "get_weather":
              return tool_result(get_weather(arguments))

• nanomcp/server.py:170-189 (helper)

  Helper function that performs live weather lookup via the wttr.in API. Called when NANOMCP_LIVE_WEATHER=1 is set.

  def live_weather(location: str, unit: str) -> str:
      encoded = urllib.parse.quote(location)
      url = f"https://wttr.in/{encoded}?format=j1"
      request = urllib.request.Request(url, headers={"User-Agent": "nanomcp/0.1"})
      with urllib.request.urlopen(request, timeout=5) as response:
          payload = json.loads(response.read().decode("utf-8"))
  
      current = payload["current_condition"][0]
      temp_key = "temp_C" if unit == "celsius" else "temp_F"
      suffix = "C" if unit == "celsius" else "F"
      condition = current["weatherDesc"][0]["value"]
      humidity = current.get("humidity", "unknown")
      wind = current.get("windspeedKmph", "unknown")
      return (
          f"Live weather for {location} from wttr.in:\n"
          f"- Temperature: {current[temp_key]}°{suffix}\n"
          f"- Condition: {condition}\n"
          f"- Humidity: {humidity}%\n"
          f"- Wind: {wind} km/h"
      )

• nanomcp/server.py:192-214 (helper)

  Helper function that generates deterministic demo weather data using SHA-256 hash of location + today's date for reproducibility.

  def offline_weather(location: str, unit: str) -> str:
      seed = f"{location.lower()}:{date.today().isoformat()}".encode("utf-8")
      digest = hashlib.sha256(seed).digest()
      celsius = 6 + digest[0] % 29
      humidity = 35 + digest[1] % 55
      conditions = ["sunny", "cloudy", "light rain", "windy", "hazy", "clear"]
      condition = conditions[digest[2] % len(conditions)]
  
      if unit == "fahrenheit":
          temperature = round(celsius * 9 / 5 + 32)
          suffix = "F"
      else:
          temperature = celsius
          suffix = "C"
  
      return (
          f"Demo weather for {location}:\n"
          f"- Temperature: {temperature}°{suffix}\n"
          f"- Condition: {condition}\n"
          f"- Humidity: {humidity}%\n"
          "\nThis is deterministic demo data. Set NANOMCP_LIVE_WEATHER=1 "
          "to try a live wttr.in lookup."
      )