When I first learned about Django signals, it gave me the same warm fuzzy feeling I got when I started using RSS. Define what I'm interested in, sit back, relax, and let the information come to me.
You can do the same in Django, but instead of getting news type notifications, you define what stuff should happen when other stuff happens, and best of all, the so-called stuff is global throughout your project, not just within applications (supporting decoupled apps).
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What you can do with signals are plentiful, and up to your imagination, so lets get into it.