What is the equivalent of a Swift completion block in Python?

Question

In Swift we can write a function with a completion block like this:

func thisNeedsToFinishBeforeWeCanDoTheNextStep(completion: () -> ()) {
    print("The quick brown fox")
    completion()
}

And then when we call it, we can put something inside of that block to execute once it's finished it's process:

func thisFunctionNeedsToExecuteSecond() {
   print("jumped over the lazy dog")
}

What is the equivalent in Python?

Answer 1

Python considers functions as objects, meaning you can pass them around (like in Swift, although I'm less familiar with the implementation details in Swift). You can't specify a type in the parameter, of course, since you can't do that with anything in Python, but that's okay. The implementation would look like:

def do_first(completion):
    print("The quick brown fox ")
    completion()

def do_second():
    print("jumped over the lazy dog.")

And then to use them:

do_first(do_second)

Unless you use asynchronous code ahead of the completion() call in the first function, the lines will execute sequentially as expected.