Leveraging Python's Implicit "return None" Statements

hey folks it's Dan Bader and today I want to talk about implicit return statements in Python Python automatically adds implicit return statements to the end of any function that you write so therefore if a function does not specify return value it will return none by default and I know this can be a little bit confusing so with this video tutorial you're gonna learn exactly how these implicit return statements work and how you can use them to your advantage and then of course also how are you gonna be able to see how they work in other people's code which is really important for understanding the Python code that's out there okay so let's start with a simple example I've got this dummy function here and it just contains a simple if statement here and we can see here in the last line it actually returns none and now with the implicit returns feature in Python you can simplify this function so let me show you a new version off this function that will be exactly equivalent so it would lead to the same output but it doesn't actually return none here it's just a bear return statement and a bear return statement in Python implies that none will be returned you might use that in some cases to simplify your code a little bit could also be confusing is if someone doesn't know about this feature so it's always something to keep in mind now because the return statement is implicit that means you can actually leave it out completely so that's what I'm doing here in this foo 3 function in this case I'm leaving out the return statement in the else part of that if statement and this will lead to exactly the same result so all these functions are exactly equivalent they have the exact same return values but you can see here that this last option is quite a bit shorter and easier to read than the first one but just to confirm that they actually all have the same output let's actually run them so what I'm gonna do here is I'm gonna go through each of those functions and I'm call I'm gonna call them with an argument of false which is going to trigger the else branch in the the central if statement here and we should we should expect to always get a none return value here so stride with the fool one function just kind of the unchanged version of that function the original version of that function so alright so this returned none now let's try it with the bear return statement that would also imply return none and again this returns none as well and now let's try it with the third function or foo 3 function here that doesn't include the else branch altogether it only has the kind of the truthy branch here and there's no return statement whatsoever so once I run this you can see here it also returns none and if I pass a truthy argument you can see here that it correctly returns the actual value so you know if I pass something else it'll just bounce that back to me and yeah I guess this is proof that this really works and I'm not just making this stuff up now of course the question that remains is when should you actually use this when is it a good idea to use this feature in your own Python code so my rule of thumb is if a function does not have a return value so in other languages that would be called a procedure then I always leave out the return statement so I don't add empty return statements if I don't have any sensible value to return right so for example if I wrote something like the built-in print function that would only ever be called for its side-effects would never return anything then I wouldn't put a return statement there it just wouldn't make any sense in my mind if you're following that principle the only time you need to decide whether or not to use a implicit return nun statement is when a function actually has a return value that makes sense from a logical perspective right so the print function we're only calling it for its side-effects but the sum function for example we want to call that because we expect some kind of return value with a function like that where it would logically make sense for it to return none I think that's where we need to discuss whether or not you should use an implicit or an explicit return on statement I think on the one hand you could say that well if you leave out the return on statement it makes the code more concise and therefore easier to read and understand and maybe you could say makes it prettier on the other hand this feature might really surprise some programmers and it they might not know that Python behaves that way when it comes to writing clean and maintainable code then using the surprising behavior is usually not the best way to go about it so for example the book that I'm working on I had a couple of code examples there or I think I had one code example there that was using an implicit return none statement and so I started getting these regular emails where people mentioned that hey then you're missing a return statement here and I have this almost like this you know template saved the way that would that I would send people as a reply was like hey you know what Python actually does these implicit return statements and that's totally ok but I can see why it's confusing and so my thinking there has shifted a bit where I'm thinking you know in this case and the book I actually changed it because the point of that code example wasn't about the missing return statement or being concise but it was more about something else entirely and being very clear and making the the example very easy to understand so in this case I think it made sense to bring back the explicit return statement I mean don't get me wrong right I love writing clean and beautiful code as much as anyone else and I used to feel really strongly that programmers should really know the ins and outs of the language they're working with but also you got to be you got to be realistic about this stuff right so when you consider the maintenance impact of even a simple misunderstanding where it's you know you're working in a in a bigger team and there's this back and forth on oh hey are missing a return statement here no I guess there's this like rule in Python that you can leave it out and then you know someone is asking about that in chat or maybe someone is tapping on the shoulder so that caused an interruption and it just you know it's it's like the butterfly effect where you have this little thing and it just kind of spirals out of control it has a much larger impact than you would have thought it would have initially and so I think when you consider the maintenance impact of stuff like that then I would be leaning more towards making the code explicit and very clear so I'm not gonna make a definite recommendation here right or like a definitive recommendation we're gonna say hey you always have to use this feature you you should never use this feature but it always depends so honestly it really depends on the circumstances but personally I try to keep in mind that code is communication and it is meant for primarily for humans not for computers otherwise we would all be writing sort of some kind of binary you know bytecode assembler language there's something like that or I wouldn't be writing Python so I always try to err on the side of being more explicit so that people have an easier time understanding and maintaining my code so you know that might not be your philosophy but I think it it really helps in making it easier to work with other people and also making your programs more maintainable in the long run all right I know I'm kind of leaving you alone here making this decision but but try it out be aware that this exists and implicit returned values are a thing in Python they're gonna come in handy and they're you're going to encounter them but also balance it with the need for being clear and writing maintainable code and actually if your philosophy when it comes to writing clean code aligns with mine and what I just described then check out my book because there are many more examples just like the one I just discussed and I'm always trying to approach it from the angle that I just explained you know where I believe that code is communication it's written for humans primarily we've got to make sure that we're writing explicit and clear code so if this is something that you're interested in learning or interested in you know improving your skills in that and kind of picking up that mindset then check out my book Python tricks I think you're gonna enjoy it alright thanks so much for listening and happy Python II [Music]