Why aren't signals simply called events?

Question

From what I can tell, in Python and and Django, signals are simply delegated events. Is there anything that functionally differentiates them from the typical notion of events in C#, Java, ActionScript, etc?

Answer 1

Actually, "signals" have been around longer than events have. In the earliest usage, a signal was an asynchronous way for processes to get notified that events had occurred. Since Unix is much older than Django (and since a lot of the Django work came from pydispatcher, where the original stuff was done), the name has stuck.

Events are really signals, you might say!

Answer 2

Signals typically have an association with an operating system facility and events are typically application-defined. In some technology stacks, the OS-level stuff may be hidden well enough that there isn't a difference in the API, but in others perhaps not.

Answer 3

Afaik Qt had the first signal/slot implementation. Qt's docs explain the metaphor: "A signal is emitted when a particular event occurs". The distinction is so subtle that the nomenclature has been blurred.

Answer 4

You might as well ask "Why aren't events simply called signals?". Differences in terminology happen.