Code-Memo

Configuration files

Python’s configparser maps to JSON/TOML/YAML via libraries, or simple encoding/json for INI-like needs when you control the format.

JSON config

type Config struct {
	Addr string `json:"addr"`
	Port int    `json:"port"`
}

data, err := os.ReadFile("config.json")
if err != nil {
	return err
}
var cfg Config
if err := json.Unmarshal(data, &cfg); err != nil {
	return err
}

Environment overrides

Load file first, then overlay os.Getenv for secrets and deployment-specific values.

TOML

Common in Go ecosystem: github.com/pelletier/go-toml/v2 for TOML files.

Flags + file

Parse flag after loading defaults from file so CLI wins:

flag.Parse()
if *addrFromFlag != "" {
	cfg.Addr = *addrFromFlag
}

Validation

Validate required fields after decode; return wrapped errors listing missing keys.

Hot reload

Rare: watch file mtime or use SIGHUP; keep concurrency-safe access to config with atomic/sync.RWMutex.