Signals minangka implementasi Django saka observer pattern — padha ngicini amanah-amanah tartamtu bisa ngabari set saka penerima nalika events tartamtu kelakon (kaya model disimpen utawa dihapus). Padha ngidini decoupled code: siji bagean saka app bisa ngreaski events ing bagean liyane tanpa coupling langsung.
Common built-in signals
pre_save / post_save → before / after a model instance is saved
pre_delete / post_delete → before / after a model instance is deleted
m2m_changed → a ManyToMany relationship changed
request_started / finished→ request lifecycle
user_logged_in / out → authentication events
