Using Dictionaries, For Loops and While Loops in Python!

hello and welcome back to the channel this will be video six in our python tutorial series so if you missed the first ones on installing and setting up python and pycharm initial introductions to variable types getting started with functions things along those lines be sure to check those out if those are concepts you're unfamiliar with we'll be using all that kind of stuff going forward in our last video we took a look at using functions so that we could repeat certain important pieces of code and in this video we're going to be looking at dictionaries while loops for loops and exponentials so what i have created what you see on the screen right now is actually called a dictionary within python as identified by these squiggly brackets um a dictionary contains what's called a key and then a value and this together is a key value pair and what that means is you can look something up inside of a dictionary by knowing the key for example if i want to print the month associated with you know january the first month and i know the key for it i type the key into these square brackets as i call the dictionary and you'll see we get january but what's also kind of nice you can use a function that python has built in called dot get so you do your list name dot get and then the key and it gives you the value and so that looks just the same [Music] but what you'll notice is you can actually the nice thing about the dot get function is you can leave a default so if it doesn't find it then you can say no key value pair exists so the the limitation of what we just did prior to this by putting the key in the square brackets is there's no if statement you know if it's either the key better exists or you're going to get an error with the dot get function you have the option of giving it a default if it doesn't exist so i'll punch in 13 and you'll see no key value pair exists and the dot get function is actually really nice when you're uncertain about your keys obviously with months that's not something there's too much uncertainty around so you really don't need the dot get if you're comfortable saying i'm pretty sure i know when my key pair exists and when it doesn't um the the applications of dictionaries are are really extensive you can use them for storing users or user data login information passwords if you're keeping something like a gradebook you could have the student and then their affiliated grade or you can have the assignment and then what score they got with the assignment the dictionary really can be used for any sort of easy lookup that you might have a whole bunch of information in one side of it and you just want an easy index value to look it up by so a really complex but doable example of a dictionary would be if you had a student name as your key so student name and then you can actually have any type of value as the value for your dictionary so you could put an entire list instead of just january you could say okay well this student got a 14 on his first assignment a 13 percent on his second assignment a 15 and a 99 because he really pulled it together near the end well if you go and you print the we have to call months because that's what our that's what our list is but if you print the value associated with the key student then what you're going to see is you get that entire list printed out so even though what i went with was months and i showed obviously a string for the key and a string for the value just know you can use anything for either of those you can use any variable type python accepts as a key and as the value pair so moving on we're actually going to dive into while loops because it goes nicely with this list and what we're gonna do is we're gonna create a while loop that is going to show us every month until we get through our list so we're gonna create a counter to do that and then we're gonna create our while loop and you you've probably seen in our previous video or you're just familiar with the way functions work while loops are fairly similar you put the keyword while and then your condition for checking this goes back to the for loops we used in previous videos as well and then you're looking for a condition and in this case we're checking that while the length and this len is a python built-in function for checking the length of objects like lists dictionaries anything along those lines anything that has a countable length so even strings have have that function where it tells you how many characters and while our counter is less than that should be less than or equals to while our counter is less than or equal to the length of the total list we're going to print out whatever the the value associated with that key is and so to do that we're going to call the string conversion of our counter because our counter is an integer but obviously these these uh keys as we defined them were strings so we're just going to convert our character string which we've talked about previously as well and then we're going to print whatever month is associated with that but what you'll see here is actually we've created an infinite loop because there's nothing that is ever going to make the counter go up so this is very important you need to put a condition that increments the counter on the end of a while statement python's actually going to see an infinite loop as an error statement and rather than let the computer crash by running a loop forever it should stop you so we're going to actually increment the counter once we've printed the months and this should there we go so just by doing that we just printed out in order every key value pair in our loop and then stopped at december and ended the code so a while loop is really nice especially if you have an application of unknown length where maybe you need every value that's inside of a dictionary but you don't even know how long the dictionary is or you're calling data from somewhere outside of your realm you're using an api or a plugin or something while loops are really advantageous a lot of game logic and things like that use while loops but they also they they need a condition like what we have in here where there's a specified and yet still open-ended things so if you were to extend the months you know for some reason they had a 13th month then this automatically is going to run 13 times and so let's say we need a loop to only run four times regardless of whether or not this changes well there's a different kind of loop that we're going to talk about now that is the for loop and a for loop is actually a little bit a little bit easier to know how many times it's going to run so you don't have to worry about the endless infinite loop scenario of a while loop a for loop you would say for i in range and you're actually defining the range of how many times it's going to run uh and you so we'll say one to four print and let's just use our months dictionary again and say print the string version of i and what you'll see immediately upon running this is we get the first one the second one and the third one a few things to talk about here the range function goes up to but does not include the end cap of your range so it does count your starting point but it does not execute this one so if you actually need a for loop to run four times you need to have the range from zero to five and so again we're using essentially the exact same we're using essentially the exact same functionality and i i could have called i anything um i know we called it counter for the while loop i could have called it counter that would be fine um and and so it's it's really doing the exact same thing if we decide to make the range up to 13 but what we have now is if for some reason some dummy adds a 13th month you know this for loop is actually just going to stop at 12 it's never going to give you more than 13. so that's just two different types of loops that's kind of good to know um but the the scenario where you would need one or the other and wouldn't be able to use whichever one you're more familiar with is fairly rare and by the time you're comfortable with loops it's the sort of thing that's going to make itself apparent so for now that's just a basic example of both loops but loops are really useful to repeat code without having to add it so what becomes really powerful is when you put functions which we've talked about previously inside of loops and that's actually what we're going to do next we're going to create an exponential scenario so we're going to say we are going to create a function and we'll call it define [Music] uh exponential and we don't need anything passed in but what we are going to do actually we do need two variables passed in we need the base number and we need the power it's being raised to and inside of the exponential function we're going to have loop so i'll go ahead and get rid of our counter loop and what think about what an exponential is doing an exponential is saying your base number is being multiplied times your base number again and that's going to be done over and over again until it's it's resulted in the power you need so so actually if you think about it what if we put a zero into this so you're going to start with a one and we're going to create a variable called answer and initially answer equals one and then counter equals zero and we will say while counter less than should this be less than or equal to we'll do less than for now let's see while counter is less than the power we are going to do this what we wrote down here we're going to do base num times itself and then the answer is going to be equal to that although actually this is counter equal to power equal to we need the answer to start out equal to the base number answer equals yeah because if we did this then every time the loop executed it would just be multiplying the base number times itself twice and that's not useful for anybody so here what we're saying is uh answer equals base num counter equals zero well counter is less than power answer equals base num times answer and we go ahead and we add one to our counter and one thing to say about what i did right here this plus equals is exactly the same thing as saying counter is equal to counter plus one python gives you the option to get rid of having to type the variable a second time and you can just tack the function right before the equal sign and that's saying it's going to add one to itself but okay let's see how close we got and what we need to tweak after this so let's just go ahead and create exponential and let's say we want three to the third power and if our code is perfect which it never is first try this would give us 27 and it gave us nothing most likely because we did not print the answer which is what we want to do at the end of our code so there we actually got 81 which 3 to the first power is three second power is nine third power is 27 so something we did answer equals base number let's try power minus one so that's 27 but let's see if we do two to the fifth 32 okay and let's try just five squared 25. okay my job is not to reinvent the wheel and create a calculator from scratch but i am just trying to show you functionality and application of while loops and how they can be used to you know rather than when we do let's make this quite a bit larger 5 to the fifth power rather than having to multiply 5 times 5 and then 25 times 5 and then 125 times 5 over and over and over again we've written the code to do it once and we've just defined the conditions for how many times it needs to happen so you can think of an exponential function really as a while loop that's maybe over simplifying it but you can see right away the power of while loops the application you could absolutely create this with a for loop as well this video is getting a little lengthy and i don't want to do that to you guys now but hopefully this was useful introduction to dictionaries while loops for loops and exponentials if you have any questions about anything you saw here today or have any ideas for videos you'd like to see in the future be sure to let me know in the comments section and hopefully you found this helpful and feel free to like and subscribe if you'd like to stay tuned for future tutorials and as always thanks for checking out the channel thanks bye you