Swift optional closure equivalent in python

Question

I'm new in Python with a strong background in Objective-C and Swift.

In swift you can create optional closures that could be use as callback. Here is a example:

class Process {
  // The closure that will be assigned by the caller of Process.
  var didSuccess: ((Bool)->())?

  func run() {
    let isSuccess = true
    didSuccess?(isSuccess) // If closure is assigned we call it.
  }
}


class Robot {
  private var process = Process()

  init() {
    process.didSuccess = examineProcess // We assign the closure
  }

  func examineProcess(result: Bool) {
    print("The result is: \(result)")
  }

  func run() {
    process.run()
  }
}

let superPower = SuperPower()
superPower.run()

As we can see when we will call 'superPower.run()' the output will be The result is: true

Is there an equivalent pattern in Python?

Answer 1

Michael Butscher posted an answer but I improved it because it could lead to some bugs.

This is the solution I use:

class Process:
  def __init__(self):
    self.didSuccess:  Callable[[bool], None] = None

  def run(self):
    if self.didSuccess is not None and callable(self.didSuccess):
    # we are sure that we will be able to call didSuccess and avoid bugs
    # caused by `myInstance.didSuccess = 3` for example
            self.didSuccess(True)

class Robot:
  def __init__(self):
    self.__process = Process()
    self.__process.didSuccess = examineProcess
    # or lambda
    self.__process.didSuccess = lambda x: print("The result is: ", x)

  func examineProcess(bool, result: bool):
    print("The result is: ", result)


  def run(self):
    self.__process.run()

I do double check on the attribute with if self.didSuccess is not None and callable(self.didSuccess) to be sure that the attribute is callable.

Answer 2

There is no real support for this. You can write something like

didSuccess(True) if didSuccess else None

In the shell this looks like:

>>> didSuccess = None
>>> didSuccess(True) if didSuccess else None
>>> didSuccess = lambda b: print("The result is: {}".format(b))
>>> didSuccess(True) if didSuccess else None
The result is: True