Always use predefined constants from `homeassistant.const` instead of string literals when accessing configuration data. For required configuration keys that must be present, use direct dictionary access (`entry.data[CONF_KEY]`) rather than `.get()` with defaults, as this provides better error handling and makes the required nature of the configuration explicit. ```python # Bad - using string literals and .get() for required keys email = user_input.get("email") password = user_input.get("password") api_key = entry.data.get("api_key", "") # Good - using constants and direct access for required keys from homeassistant.const import CONF_EMAIL, CONF_PASSWORD, CONF_API_KEY email = user_input.get(CONF_EMAIL) password = user_input.get(CONF_PASSWORD) api_key = entry.data[CONF_API_KEY] # Will raise KeyError if missing, which is appropriate ``` This approach improves code maintainability, prevents typos in configuration key names, and makes the required vs optional nature of configuration values clear through the access pattern used.