Start with hardcoded values

custom_components/irm_kmi/__init__.py

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+"""Integration for IRM KMI weather"""

custom_components/irm_kmi/manifest.json

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+{
+  "domain": "irm_kmi",
+  "name": "IRM KMI Weather Belgium",
+  "codeowners": ["@jdejaegh"],
+  "dependencies": [],
+  "documentation": "https://github.com/jdejaegh/irm-kmi-ha/",
+  "integration_type": "service",
+  "iot_class": "cloud_polling",
+  "requirements": [],
+  "version": "0.1.0"
+}

custom_components/irm_kmi/weather.py

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+import logging
+from homeassistant.components.weather import WeatherEntity
+from homeassistant.components.weather import ATTR_CONDITION_PARTLYCLOUDY
+from homeassistant.const import UnitOfTemperature
+
+_LOGGER = logging.getLogger(__name__)
+
+
+def setup_platform(hass, config, add_devices, discovery_info=None):
+    add_devices([IrmKmiWeather()])
+    _LOGGER.warning("Irm KMI setup")
+
+
+class IrmKmiWeather(WeatherEntity):
+
+    @property
+    def name(self) -> str:
+        return "IRM KMI Weather"
+
+    @property
+    def condition(self) -> str | None:
+        return ATTR_CONDITION_PARTLYCLOUDY
+
+    @property
+    def native_temperature(self) -> float | None:
+        return 20.2
+
+    @property
+    def native_temperature_unit(self) -> str:
+        return UnitOfTemperature.CELSIUS