How To Use Sets in Python (Python Tutorial #13)

Key Takeaways

hi everyone in this video I'm going to show you how to use sets in Python now what is a set well in Python a set is a type of data that stores a set of things and this is actually a set of unique things so for example if you have a set of these two numbers 1 & 3 and if you try to add another number 3 here to this set nothing happens and you still have this set 1 & 3 because a Python set just rejects any duplicate elements ok let's take a look at some code examples here if you write a eCos set parenthesis this creates a new empty set and then it assigns it to this variable a so if you print a by writing print a and then once you run the cell this thing is printed set parenthesis this just represents an empty set all right and to add elements to this set for example a number you can just write a dot add parentheses 1 and this as the number 1 to this set so once you print a you see this thing curly brackets and then 1 inside this just represents a set with only one inside the set and after that if you write a dot add 2 you'll add 2 to this set and I want to print a again you see that now this is a set of two numbers 1 and 2 and then if you try to add the number 2 again by writing it I add 2 nothing happens and you still get the same set because again a Python set rejects any duplicates ok one useful thing to do with a set is to iterate over every element in the set so you can do that with 4 X in a and then print X so you see that this is exactly the same as how we iterate over each element in a list so if a was a list you know this part will look exactly the same and this way we can iterate over every element in the given set a so let's see if you works by running the cell and it does we see 1 & 2 being printed ok so when should you use a set one example is when you want to remove duplicates from let's say a given list so let's say you're given this list called given list one with these elements 1 1 2 4 & 2 here if you want to remove the duplicates you know these two ones and these two twos so that you only have 1 2 & 4 and let's say a new list you can use a set here to do that you can just write this first create a new set by writing new set let's say 1 equals set parentheses this creates an empty set and then after that you can go over each element in the given list by writing for X in given list 1 : 4 spaces you set 1 dot add X so this way we're saying we want to add each of these elements 1 1 2 4 & 2 to this new set use that one and after that you just need to print new set 1 and what do you think we're gonna get we'll get 1 2 & 4 because we're adding every element in the given list but this set automatically rejects any duplicates and that's why we're left with these unique elements okay and what if you want to create a new list that only contains these unique elements from the original list think about it for a second and here's my solution first create a new list by writing new lists 1 equals square brackets this creates a new empty list you can do the same thing by writing lists parentheses as well and then go over every element in the set in this set 1 2 & 4 by writing for X and you set 1 : 4 spaces new lists 1 the append so this way we're going over every element in the new set one and then we're appending that to new list one by writing new list one dot append X so after that once you print new list one you should see this list one two and four and just a quick note here you can add things to a set there are not numbers so for example you can do this B equals set this creates an empty set and assigns it to be and then you can write beta add single quotes Apple and then be the add single quotes banana and this way we're adding the strings apple and banana to this set and you can even mix multiple types of things in a single set so you can do add one and then this as apple banana which are strings and one which is a number two the same set B so once you print B you should see this one banana and apple okay and I think one thing to note here is that you know the order in which you see these elements one banana and Apple is different from the order in which we added these things apple banana and then one so a set is a type of data that doesn't store the order in which things have been added to the set and that's one way in which a set is different from a list in Python and that's because when you add things to a list by using the append function like we saw earlier here the order in which these things have been added to a list is preserved okay let me give you a simple exercise problem to practice using what you just learned so let's say you're given this list given a list - and with these elements one three four one and three the problem is can you find the sum of unique elements in this list so the unique elements are obviously 1 3 & 4 and the sum of those elements is 8 so your solution should be able to find this number eight and your solution should work no matter how many elements are in the given lists so think about it for a second and I'm gonna give you my solution in a second okay here's my solution first create a new set by writing new underscore set to eCos set parenthesis and then run a for loop over given list two by writing for X in given list two : new set to dot add X so this way we're adding all the unique elements to this set so after this for loop this is gonna have the elements one three and four and to find the sum of those elements there's actually a shortcut for it in Python you can just write some new set too but here let's not use that for now and let's do it in a more explicit way so we'll first create a new variable called the total and then let's set it to zero and then we'll just add every element in new set to two total we can do that by writing for X and you set two : total plus equals x so this way we're adding each element in new set to which were calling X two total and once you print total you should get eight let's see if it works and it does okay that's it for this video thank you as always for watching my videos and I'll see you guys in the next one