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

The relevant spot in the docs:

callback - callback function which will be called with argument 
        list equal to callbackargs+(result,) 
        as soon as calculation is done
callbackargs - additional arguments for callback function

So, if you want some code to be executed as soon as the result is ready, you put that code into a function and pass that function as the callback argument. If you don't need other arguments, it will be just, e.g.:

def itsdone(result):
  print "Done! result=%r" % (result,)
...
submit(..., callback=itsdone)

For more on the callback pattern in Python, see e.g. my presentation here.