Parallel Python: What is a callback?

Question

In Parallel Python it has something in the submit function called a callback (documentation) however it doesn\'t seem to explain it too well. I\'ve posted on

Answer 1

A callback is a function you define that's later called by a function you call.

As an example, consider how AJAX works: you write code that calls a back-end server function. At some point in the future, it returns from that function (the "A" stands for Asynchronous, which is what the "Parallel" in "Parallel Python" is all about). Now - because your code calls the code on the server, you want it to tell you when it's done, and you want to do something with its results. It does so by calling your callback function.

When the called function completes, the standard way for it to tell you it's done is for you to tell it to call a function in your code. That's the callback function, and its job is to handle the results/output from the lower-level function you've called.