Sets in Python - Advanced Python 04 - Programming Tutorial

Key Takeaways

hi everybody welcome to a new python tutorial today we're gonna talk about sets in Python a set us a collection data type that is unordered and mutable but unlike lists or tuples it does not allow duplicate elements a set is created with braces just like a dictionary but we don't put key value pairs in it but instead just single elements separated by a comma for example let's put some numbers in here and print this and we will see our set here and if we put for example another one and then add a two here and print this again then we see that only one of each element is kept because a set does not allow duplicates we can also use the set function and use an iterable here for example let's use a list here this will also create a set or we can use a string here for example hello and if we print this first of all we see that the order is arbitrary because asset is unordered and the order is not important and we also see that there's only one L in our set so this is a nice little trick to find out how many different characters are in your word now if you want to create an empty set and you do it like this just with the braces then you have to be careful because now if you have a look at the type of this then we see that this is recognized as a dictionary so if you want to have an empty set you have to do it with the set method a set is mutable so you can change it later on so now we can add elements and we do this with the dot add method so let's put in some numbers here and print this and we can also remove elements again with the remove method so let's remove the three and if we want to remove an element that is not inside our set then this will raise a key error so be careful here so there's another method that's called at this card method that that's the same thing so it also removes the element and if it does not find the element then nothing will happen so no arrow here we can also use the clear method of course this will empty our set or we can use the pop method so this will return an arbitrary value of our set and also removes it so if we print this then we see in this case it returned the one and also remove the one from our set now we can iterate over our set very easily within for in loop so for I in my set and then do something in this case just print this so this will iterate over each element and print it and we don't have to call this I we can also call this for example X or whatever we want now we want to check if an element is inside our set we can do this with an if in statement so if one in my set and then we print yes so the one is an our set the two is an our our set and if we check for example for the four then nothing gets printed now let's talk about Union and intersection and for this case first of all let's create three different sets one with odd numbers one with Eve numbers and one with prime numbers and now we can calculate the Union so the Union combines elements from both from two sets without duplication so let's calculate the union of odds and we do this with dot Union and then as an argument the second set so evens and print this then we see that now we have all the numbers from zero to nine so the Union will combine elements from both from two sets without duplication we can also calculate the intersection of two sets so the intersection will only take elements that are found in both sets so if we say the intersection equals odds dot intersection evens and if we print this then we will get an empty set because odds and evens don't have the same elements now if we calculate calculate the intersection of odds and Prime's we will get all the prime numbers that are also also 3 5 7 if you calculate the intersection of evens and Prime's then we will get back only the even prime numbers so in this case only the two now we can also calculate the difference of two sets so let's create two different sets again set a with numbers from 1 to 9 and set B with walk with 1 2 3 10 11 12 now the difference will return a set with all elements from the first set that are not in the second set so let's call the call it if equal set a dot difference set B and print this then we see that we will get back the numbers from 4 to 9 because it takes the elements from our first set but not the ones that are also in the second set so only from 4 to 9 so if we do it the other way around set B dot difference set a then it will take 10 11 12 but not these 3 numbers because they are also here so then there's a second different method a second difference method that's called the symmetric difference method so the symmetric difference method will return a set with all the elements from set a and set B but not the elements that are in both sets so again so it takes 4 5 6 7 8 9 from set a and 10 11 12 from set B but not 1 2 and 3 because they are in both sets so if I use set a symmetric difference set B then this is the same thing now Union and intersection and the difference method that I just showed you they will not modify the original sets they always will return a new set but we can also modify our sets in place so for example we can say set a dot update set B and now print our set a then we will see that this updates the set by adding the elements that are found in another set so without duplication again so it does not add one two and three again but it adds 10 11 and 12 there's also a intersection of an update method so set a dot intersection update set B and what this does it updates the set by keeping only the elements from found in both sets so only 1 2 & 3 are found in both sets so only these numbers remain in our set then there's also the difference update method so set a difference update set B and if we print this we will see the numbers from 4 to 9 because difference update it updates the set by removing elements for found in another set so it also it found it finds 1 2 & 3 in the set B so it removes these numbers from our set a and then there's the symmetric difference update so this updates the set by only keeping the elements found in set a and in set B but not the elements that are found in both so 1 2 & 3 are found in both sets so these are not taken but then it takes all the remaining elements from both sets yeah you have probably have to play around with them yourselves a little bit to make it Kira and yeah let's also talk about subset superset and disjoint methods so for example let's make them a little bit smaller you can calculate the if set a is a subset of set B and if we print this then this will return false because subset means that all the elements of our first set are also in our second set so if we use it the other way around set B is a subset of set a then this will return true because 1 2 & 3 are also in the second set and the opposite is called the superset method so is superset and in this case it returns false because a superset returns true if the first set contains all the numbers or all the elements from the second set so set B does not contain 5 4 6 so it's not a superset but set a is a superset of set B because it contains 1 2 & 3 and we can calculate if two sets are disjoint so this joint returns true if both sets have a null intersection so no same elements so set a is this joint set B and if you print this this will return false because they have same elements and if we create for example a set C and put 7/8 in here and check set a is this joint with set B then this will give us true now let's briefly talk about copying two sets if you have watched the previous episodes about lists for example then you already know this you have to be careful when you want to copy two sets and only do this with a simple assignment so let's say let set B equals 2 set 1 set a first of all if you print this then we see that we have a copy but now if we modify the copy let's say set B add 7 and if we print the copy and also print the original 1 then we see that also the original 1 changed because with this simple assignment both point to the same set so be careful here you only copy the reference now if you want to make an actual copy you have to use the dot copy method so if you run this again and we see that the original set didn't change or you can also use the set method and use the first set as a argument this will also make an actual copy now as a last thing I want to show you the frozen set the frozen set is also a collection data type and this is just an immutable version of a normal set so you create this with the frozen set method and there's an argument you can also put an iterable here for example a list and let's print this then we see our frozen set here so with a frozen set you cannot change it after its creation so if I try to do a dot add two this will give us an error or i can also say try a remove one this will also give us an error or any of the updates update methods I showed you they also don't work but for example Union intersection and difference method they will work so yeah that's it about sets and frozen sets and I hope you enjoyed this tutorial and see you in the next tutorial where we talk about strings in Python