Why are empty functions ever needed?

Question

def func():
    pass

Can anyone describe the use case or give a real time example of the usage of empty functions in python?

Are you really asking why they are _needed_, or are you asking why they are _possible_? — Bryan Oakley, Aug 30 '18 at 14:43
An empty function is equally useful or useless in any language. Is your real question perhaps rather why *`pass`* is needed? — deceze, Aug 30 '18 at 14:44
I have started learning python recently, I could get what exactly pass is used for but I couldn't follow this concept of empty functions and the need for their usage in any code in real time. — PoojaPracash, Aug 30 '18 at 15:09

score 2 · Answer 1 · 2018-08-30T14:41:51.040

2

One might make empty functions to sketch out a high-level overview of an algorithm, then go in and work on the various functions later; a placeholder basically.

edited Aug 30 '18 at 14:41

answered Aug 30 '18 at 14:39

That's not a good example. You can simply remove it from your `Animal` class and it will work fine. – spectras Aug 30 '18 at 14:40
As is, this isn't a compelling example, since `Dog` and `Cat` will work fine even if `Animal` doesn't define a do-nothing `makeSound`. If `makeSound` is an *abstract* method, though, it makes more sense. – chepner Aug 30 '18 at 14:40
2

I would rather put `raise NotImplementedError` in `makeSound()` of `Animal` – abc Aug 30 '18 at 14:41
Well python is so flexible it woun't mak any problems removing makeSound from animal but if you are working with an advanced IDE and autocomplete you may want to add the makeSound funktion to your animal class so the IDE knows what to autocomplete – Phillip Aug 30 '18 at 14:42
The idea was that someone get an idea of what Animal's children might implement by glancing at the Animal class – Aug 30 '18 at 14:43

score 2 · Answer 2 · answered Aug 30 '18 at 14:41

It's arguably whether or not they are "needed", though they can be convenient.

However, I think most would agree that the pass statement is needed, and function definitions are needed, and what python doesn't need is a special case that prevents you from using pass as the only statement in a function.

score 2 · Answer 3 · answered Aug 30 '18 at 14:49

An empty function definition is equally pointless or useful in any language, there's nothing specific to Python here. You may write empty functions in any number of circumstances, from needing a dummy function for testing, for sketching out code, for an abstract class and whatnot.

The only special thing here is Python's pass, which is simply a syntactical requirement. Where in other languages you may write function () {}, Python requires you to delimit the function using whitespace and indentation, so you must write something there. And instead of letting everyone define their own convention of how to deal with this situation, pass exists.

score 1 · Accepted Answer · answered Aug 30 '18 at 14:49

Here is a real example from a project of mine.

The project allows the user to configure arbitrary actions, that can be passed to various parts of the program, so they can trigger a customizable response to specific events.

The user might also have no interest for some events. Yet specifying an action is mandatory, otherwise every single use of an action in the entire project would have to test for None, that's error-prone).

Thus the DoNothing action:

class DoNothing(Action):
    async def __call__(self, context=None):
        pass

(if actions were simple functions it would just be def DoNothing(): pass but my actions have other methods, which DoNothing doesn't need to override).

Why are empty functions ever needed?

4 Answers4