"is" vs "==" in Python – What's the Difference? (And When to Use Each)

Key Takeaways

hey what's up folks it's Dan Bader here and it's time for another python video so I'm doing this new series of videos uh with little python tidbits you know really cool features in Python that you can apply in your own code in your day-to-day work and that are just going to give you a deeper understanding of python and I'm I'm calling them python tricks so this is a new video series I'm starting and um Shameless plug I'm also working on a book under the same name which is going to be almost like a a a buffet of really awesome and cool features in Python that you might not have heard about or you know that you've always been curious about uh about how they might work so I'm actually working on this book in uh In Like An Early Access or like beta mode so you can get updates as they come out and you can get in for a cheaper price and if you're interested I'll I'll put the link into the video description below all right so in this episode of python tricks I want to talk about the difference between the is operator and the equals equals operator because I know that um there this is often a point of confusion for python developers and um I've been trying to come up with you know an example that really boils it down um to to like a minimal example necessary to understand this distinction and I think I got a pretty good shot at this so so bear with me so at the end of the video you're going to know the difference between is and equals equals and you're going to know when to apply them so the key thing here is that there's a difference between two things being identical or two objects being identical and them being equal like there's a semantic difference there's a difference in meaning and so for example when I grew up our neighbors had uh twin cats so there were two cats that looked pretty much exactly the same but of course they were they were two different cats I mean they were not you wouldn't say like oh that's the same cat right that would be crazy because there's two of them and I'm going to keep stretching that analogy even thinner so bear with me right so there are two different cats and uh they're two different entities but they look the same like you could say oh they're they're equal but uh really what this example shows is that there's a difference between something being two things being equal and two things being identical and that difference is really important if you want to understand and the difference between is and the equals equals operator so let's start with the equals equals operator first so this guy here it Compares by checking for equality so if these cats were python objects and we compared them with the equals equals operator we'd get hey these cats are equal as an answer because they you know they have the same properties they look the same now on the other hand the is operator Compares identities so if we compared our identical like seemingly identical cats or identical looking cats with the is operator then we'd get the answer that well they're two different cats right they're not the same cat like there's two of them like are you crazy so before I get all tangled up in this cat analogy um let's actually come up with some python code here so what we're going to do first is we're going to create a new list object now just um create this new list one two three and then we're going to create another variable that points to the same list so now these two variables A and B they're pointing to the same list so when we inspect a you can see here okay this is the contents we well we put in earlier and if we inspect uh B then we get the same result now at this point we we know that they kind of look the same right so if we compare them with the uh equals equals operator we get true as the answer because well you know they they look the same they have the same uh seemingly the same content now what that doesn't tell us however is whether or not A and B are actually the same object I mean in this case we know because we created them and we assigned B to point to uh the the same object that a points to but suppose we didn't know right like how could we find out and this is where the is operator comes in so if we went a a is B then in this case python would tell us yeah they're the same object like they are the same thing and uh that would mean you know if I go in and uh change a by let's say putting in a string if I change a that would also change B because they're pointing to the same underlying object right and so now um I'm actually going to undo this and just you know create create a new list here and then replay everything I did before so now we're you know I undid this change here where I added this string so what we're going to do now is we're going to create a new copy off the this list that we're going to call C and the way we can do that is just by calling uh the list function or the built-in list function on a again what that's going to do it's going to create a shallow copy that will look exactly the same so let's take at look at a again look at B again and then look at Z and you can see here they all look exactly the same right if you just looking at their contents they look exactly the same so now this is where it gets interesting right because when I go and compare a to c then we get the answer okay they're they look identical uh they are considered equal now if I go and do a is C then we get a a different result because python tells us hey they're not the same object they might look identical but they're not the same freaking cats they're two different cats that just look the same right they're both like they both have black fur and the same uh eye color and whatnot but they're they're two different cats and really this is the key distinction between equals equals and the is operator because the is operator or an is expression it evaluates to true if two variables point point to the same like identical object and the equals equals operator or an equals equals expression evaluates to true if both objects are equal or have the same contents but they're not necessarily the same object like we don't care about that all right so I hope this clarified this difference to you and uh just think of cats so every time you're going to have to make a decision between equals equals and is just think of twin cats I mean think of cats all day you can also think of dogs it works the same way with dogs but that's really the key distinction you need to remember all right so I hope this was helpful uh like I said if you enjoyed this kind of micro example where I'm explaining an aspect of python part of the language um in sufficient detail to kind of you know get started with it and really understand the underlying principle then uh be sure to check out my new book it's available for Early Access right now and I think you might really enjoy it cool talk to you soon thanks so much