Python Crash Course For Beginners

[Music] hey what's going on guys welcome to my Python crash course for beginners now I did a crash course about a year ago and we use the Eclipse IDE and what I've always hated about that video is the unnecessary amount of time that I took just to set up eclipse it was like 10 10 12 minutes or something like that and I wouldn't even suggest using Eclipse anymore we're gonna be using vs code which is what I use for virtually everything I do I also miss some things and it just could have been a better video so we're actually gonna just jump right into it and what I'm doing is using the Python sandbox which is actually from my django course on udemy I'll put a link in the description if you're interested on in that and if you look in here and that the link to this is in the description to this repository so we just have a bunch of Stata files for certain things we'll be looking at like strings functions classes and they basically have nothing in them but maybe some comments and we're gonna add to these as we move along so you might want to download the sandbox and go ahead and open it up in vs code or whatever our text editor or IDE that you're using so as you can see I already have all the files open here and we're going to be starting with variables dot pi so you can go ahead and open that now obviously you need to have Python installed so that your system can interpret the Python code so you need to have python 3 which you can get from python or just go to downloads I'm on a Mac so I would just click here if you're on Windows you can download the Installer so you just want to get that installed and then open up a terminal vs code has an integrated terminal that I'll be using and if you say python - - version on a mac you're probably gonna see python 2.7 which is not what we want to use once you install python 3 if you say python 3 - - version you'll see either 3.7 or whether it's a later version or whatever as long as it's version 3 if you're on Windows you'll probably see version 3 with just Python ok so whatever whatever is version 3 that's what you want to run your file so let's clear this up and we'll get started so this variables dot pie we're gonna go over a couple things we're gonna go over how to define variables some of the rules and also data types okay because just like with any language there's a bunch of different data types we're only going to look at the more common ones there's there's others that aren't used very much I'm not going to get into this is a crash course but basically a variable is a container for a value which can be various types and if you've if you know any other language I'm sure a lot of you guys know JavaScript if you've been following my channel you know what a variable is okay so before we talk about variables so I just want to quickly look at how to comment in a Python file and by the way your Python file should end with a dot pi extension so a number sign or hash tag whatever you want to call this this is how you can do it's just a regular comment just a single line comment these triple quotes whether single or double these are called doc strings and they're often used to define functions so you'll see these a lot in function declarations but they can also be used for multi-line comments as you can see here so let's go over some of the variable rules that are the naming conventions so there case-sensitive if you create a variable called name all lowercase and name all uppercase these are going to be different variables okay they must start with a letter or an underscore they can have numbers but they cannot start with a number and that's a very common rule for variables in in many different languages alright so let's start off by creating some variables so I'm going to create one called X and I'm gonna set it to one and now in Python there's no semicolons so if you're coming from JavaScript even though you don't need semicolons in JavaScript most people do use them coming from PHP or Java or any language like that you're probably used to semicolons so you might find yourself screwing up a little hair in there and putting in a semicolon I know I still do it but yeah no semicolons also when we declare a variable we don't have to do like var or anything like that there's an special symbol like PHP it's just simply the whatever you want has the variable we also don't have to do like int or anything like that now this is going to be casted as an int by default so I'm just going to put the the variable type here of int and I'm gonna set another variable of Y and I'm gonna set that to 2.5 so this is actually a float okay or a floating-point number next one is going to be name and I'm gonna put some quotes here and we'll say John and this is actually a string or an STR is the official type I just put these I want to make this nice and neat just so you guys can have this as a reference later on and I will have the finished version in the github as well and by the way strings can have single quotes or double quotes but I prefer a single and let's do is cool and we'll set that equal to true and this is a boolean or a bool okay now it's important to know that with ilion's you want to have a capital t for true or a capital F for false if I do that it's it's gonna be looked at as a variable called true which doesn't exist okay so those are the main types that you'll be dealing with so there's an easier way if we want to declare all these variables we can actually do a multiple assignment so let's go ahead and say multiple assignment and again I'm gonna put a lot of comments in this code in in the sandbox just so you guys have it as a reference so let's say we want to do exactly what we just did above we could say X Y name and is cool and we could set that to a set of parentheses and then we can put the values so one and two point five string of John and a boolean of true so this line here does exactly what we did up here only it's it's more compact okay so let's go ahead and output something so in Python we have a function called print that we can use now if if you've ever used Python 2 you might see something like print hello in Python 3 you want to make sure that you use parentheses okay so we want to go like that so if I run this file by saying python 3 and the name of the file which is variables dot pi we get hello okay if i want to output one of these variables like x we'll go ahead and run that we get 1 we can also output multiple things so we'll do XY name is cool and we'll run that and you can see it will output all that stuff all right and of course we can do most of the stuff that you can do in any other language like for instance basic math I could create a variable called a and set it to X plus y and if we wanted to add a on the end of this print right here and run that you'll see we get 3.5 now we can also check the type so let's say we wanted to check the type of X we would do a let's do a print and in here we're going to use the type function so we're going to say type and X and let's see what that gives us so it gives us this class int ok so the type is going to be in here now there may be cases where you want to cast a different type to a value like let's say we want to make X which is an int of 1 let's say we want to make that a string of 1 so we can do casting so I'm going to set X equal to and then I'm gonna use STR okay so we can use the type and then pass in whatever we want to turn into a string which is X itself and then I'll go ahead and run this and now you can see that we get class STR if we want to change let's say Y which is a float into an int we could say y equals int and we'll pass in Y and let's print out y and let's also the type of while it's also print out y itself okay so what we have now is int y is now an int and then we just get two okay so it went from two point five to two because an int is a whole number whether or negative or positive let's say we wanted to change Y back to a float okay so Y is now an int of two so I'll create a new variable called Z and let's say float and pass in Y and let's see what we get for the value of Z as well as the type of Z and we get a class of float and the value is 2.0 okay it's not going to go back to 2.5 because when we change it to an int it was then turned to 2 and then we turned it back to a float so it's gonna be 2.0 okay so hopefully that makes sense so we're gonna move on I don't want this to be too too long I want to keep it under 90 minutes so we're gonna move on to strings okay so let's open up strings dot pi and what I really want to go over is is like inserting variables into strings formatting them and I want to look at some of the string methods and how how we call those okay all strings have methods attached to them and we're going to look at some of those so let's set a variable up here a couple variables one of name will say Brad and let's do age which will be an int of 37 okay now to concatenate which means basically to insert a variable into a string we do that pretty much the same way that we wouldn't JavaScript so we could say like hello my name is space and then we'll put a plus sign just like we would in JavaScript and then if we run this with Python 3 strings dot PI we get hello my name is Brad now let's say we want to put the age in there as well so we would concatenate back to a string and I am space and they'll put a plus sign and the age variable and let's see what happens when we run that so we get an error because we can only concatenate string or STR and age is an int so what we would do in this situation if we really wanted to do this is we would cast this to a string just like I showed you in the last file so we just wrapped that in STR and run it and now it works now there's better ways to to do this to insert variables into into strings so we can do string formatting and one way is to do positional arguments so let's say arguments by position and we're gonna say print and I'm gonna put these curly braces in here okay actually you know what we'll do let's yeah let's just do my name is and then I'm gonna put curly braces and then name and I am age okay and then what we want to do is call the format method so we do dot format and then we can set name equal to name which is this variable up here okay and then we're gonna set age equal to the age variable so these are just basically placeholders so whatever whatever is in this whoever is in this right here should show up here when we run this so I'm gonna comment this one out and then run the file and we get the same thing my name is brad and i am 37 and notice we didn't have to do any string format casting or anything like that now this is one way to do with this there's another way and that's using f strings okay now f strings were they're only available in python 3.6 and after okay so if you're using an earlier version you shouldn't be able to use f strings but they're pretty convenient so basically what we can do is just put an F right here and then put our quotes and say hello my name is name and I am age now that's all we need because what's going on is this is an actual variable that's up here so we're directly putting the variable into the F string name and age so if we go ahead comment that out and run this we get hello my name is Brad and I am 37 all right so pretty pretty easy and it's this is very similar to JavaScript template literals only instead of using backticks we just put an F right here in front and we don't use the money sign like that okay I'm going to be making a lot of references to JavaScript cuz I know you know that's that's mostly what I do on my channel so I know a lot of you guys are JavaScript developers alright so let's move on here I'm going to comment that out and I just want to look at some string methods and how we how we do that so let's set a variable of s and I'm just going to set it to hello world all lowercase and let's say we want to capitalize string so we can cut we can actually use a method called capitalize so I'm going to do a print and then all you have to do is take that string and then dot the met whatever the method is in this case capitalized okay make sure we put parentheses okay because it is a it's a method which is basically a function so let's go ahead and save that and we'll run it and we get hello world and notice that the first letter is capitalized that's what it's going to do now I have some other methods here that I want to show you what I'm not going to take the time to type them all out because they're basically used in the same way it's just dot and then the method so I'm just gonna paste them in and go over them real quick so we have upper which is going to make all uppercase make all your characters uppercase you also have lower we have swapped case which will swap the cases this is this Len is actually a function that can be you dawn strings list spec basically any data type and it's gonna get the length so in this case it would get the the amount of characters in the string we also have a replace method so if we wanted to take the word world and replace it with everyone if we were to print this out it would say hello everyone count so if we want to have a substring like just H we could count the number of H's inside the string starts with is going to return a true or false value based on how it starts so this would return true because our string does start with Hello ends with is the same thing only it's going the other way its ends with this would return true because our string does end with D split is going to take our string and turn it into a list which is basically an array and it'll have all the words in the list okay find find is going to find the position of a character so in this case it's going to look for the first R it's going to give you the number basically the position number is alphanumeric alphabetic and numeric these are all going to return either true or false based on if all the values are either alphanumeric alphabetic poor numeric okay so let's go ahead and run this and it's just gonna log all of the prints that we have here so basically this this list right here is from the split so it splits hello world into a list find its gonna look for the position of the first R which as you can see is 8 all these the alphanumeric alphabetic in numeric these will all be false and the reason for that is because of the space if I were to get rid of that space it's now alpha and alpha numerics so we should get true for those two so if we run that again you'll see we have true for both alphanumeric and alpha of course it's gonna be false for numeric all right so yeah I mean there's other methods as well I just wanted to give you some examples of some of the string methods so let's go ahead and clear this up and let's move on so we're now going to talk about lists which are very very important in Python they're basically like arrays so if you've dealt with JavaScript or PHP and many other languages it's similar to an array okay so let's first just create a list and in the the definition is a collection which is ordered and changeable they also allow duplicate members okay there's other data types that for instance are unordered and don't allow duplicates and we'll get into some of those in a little bit but let's go ahead and create a list so I'm gonna say numbers variable called numbers and we'll set it to some brackets and we'll just put a bunch of numbers in here okay so that's one way to do it we can also use a constructor so I could say let's do numbers too and we'll set that to the list constructor and this is actually going to take in another set of parentheses and then we can put our values in like that okay so this is gonna both of these are gonna create the exact same thing a list with 1 through 5 so if I go down here and I go ahead and print numbers and numbers 2 and we run this file with Python 3 list dot PI you'll see that they're both the same really but this I don't really like doing it this way I don't really like using constructors it's just like in JavaScript when you can say like new array and then put your array and which I don't use either so this is a the more common way to create lists all right now I'm actually going to create another list called fruits and this is the one we're going to work with so this is just gonna be an array of strings like apples oranges will do grapes and pears all right so we have a list of strings now I want to go over some of the stuff that we can do here such as a single value from a list so to get a value let's do a print and let's pass in the name of the list which is fruits and then we just want the index of whatever it is we want let's say we want oranges we would use one for that and the reason we use one is because lists are zero base ok just like pretty much any array in any language it's going to be 0 1 2 and so on so if I go ahead and run this we get oranges now let's say we wanted to get the length of a list so for that we use the same Len function that we used in for a string we just do Len and then pass in fruits ok so if I go ahead and run that we get 4 because it's 4 I for items or values in this list let's say we want to add to it or I should say a pen do we want to add to the end of the of the list so we'll say a pen to list and we could do that by just saying fruits dot append and then whatever we want let's say mangoes and down here we'll just go ahead and print fruits and let's run this oops and it's just gonna go ahead and add mangoes to our list and then print it out all right at the same time we can remove stuff so let's say remove and we'll say fruits dot remove and then we can simply put the value in let's say we want to remove grapes ok so if I save this and we go ahead and run it notice that grapes is now gone if we want to insert it into a specific a specific position not just append it we can use insert ok we'll say insert into position so say fruits dot insert and we want to pass in where we want to insert it which is going to be positioned too and then the item we want to insert which is strawberries all right so let's save that and let's run it now you can see strawberries is now in position to zero one two now we can also remove from certain positions so a Pierre we use from the remove method and we pass in the value we can also remove it by the position by using the pop method say remove with pop so say fruits dot pop and let's take strawberries out which is in position two okay so if we run that now you can see strawberries is gone we can also reverse the list by saying fruits dot reverse you run that now you can see that mangos is first and apples is last we can also sort okay if we want to sort alphabetically we can say fruits dot sort and if we run that you'll see it's now in alphabetical order you can also reverse sort by same thing just calling sort but passing in reverse equals the boolean of true and now if we do that you can see it's sorted in the opposite direction all right so there's other stuff there's other methods and stuff but these are some of the the really popular ones oh if you wanted to change a value you could do that as well so let's actually let's say fruits and we'll say the first value we want to change that - I don't know blueberries okay so if I run that you'll see well I mean we're doing a reverse sort so it's at the end but it replaced apples which was in the zero position with blueberries okay so that's list let's move on now to tuples and sets okay so we want to go to tuples underscore sets dot pi so a tuple is a collection which is ordered and unchangeable okay and also it does allow duplicate members the important thing here is unchangeable okay so let me give you some examples I'm gonna clear this up down here and let's create a tuple so we'll call this fruits just like we did with the array and to create a tuple you want to use parentheses okay I'll say apples oranges and grapes now you can also use a constructor just like you can with lists and just about any other data type so I could say equals tuple passing another set of curly braces apples oranges and grapes alright and if I want to print fruits and fruits too and we want to run Python 3 tuples underscore set stock pi and there we go so they're both the same thing and I don't again I don't really use the constructor so one thing to remember with tuples is if you only have one value you want to leave a trailing comma okay so if I say fruits 2 equals and I go just apples like that and what I'm gonna do is I'm going to print out fruits 2 and I'm also gonna print the type okay so I'm going to say type fruits 2 and let's see what that gives us so it gives us apples no parentheses around it and it says class string okay so if you don't have the trailing comma it's gonna look at it as a string if I put a trailing comma like that even though it looks a little weird if I run it now it's 4 you can see it's a it's clear a tuple and it has a class of two bull ok so just remember that let's say single value needs a trailing comma all right so to get a value from a tuple it's just like he would with a list so we could say print let's say fruits one get rid of this and we'll run it and we get oranges because oranges in the one position now I showed you with a list actually let me just put a comment here I showed you that with a list we could say like fruits grab one of the indexes and change it to let's say pears but with tuples you can't you can't change the value okay just right up here it says unchangeable so let's see what happens when we when we run this we get this type error and it says tuple object does not support item assignment okay tuples cannot be changed let's see what else if we want to delete a tuple or anything really we can use the del method so we can say del let's say let's do fruits 2 and then if we were to print fruits to see what happens you know see it says right here wait actually it's still giving us the error from this so I'm going to comment that out and run it and it says fruits 2 is not defined okay we did define it up here but we deleted it completely so now it's it's no longer defined all right we can also use len with with tuples so let's get the length of fruits and it'll go ahead and run that and we get three okay so fruits has three items in it all right so let's move on to sets so we clear this out now a set is a collection which is unordered okay so it's unordered and it's unindexed there's no duplicate members okay so I'll show you exactly what that means but to create a set let's use fruits we already use fruits up here let's just we'll do fruits set and a set is created with curly braces and I mean you kind of have to decide when you're when you're programming you have to decide what the best data structure is to use should you use a list you should use a set tuple I mean every situation is different in some work in in certain situations and some don't I mean if you if you don't want to have duplicate members then a set might be what you're looking for but I'm not going to get into all of that stuff this is just about syntax and learning the basics so a lot of times you'll want to check if something is in a set and there's a lot of different ways to do this but we can just say apples in fruits set and that's going to return either a true or a false so if we run that you'll see it returns true cuz apples is in the fruit set we can also add to set and we can do that by saying fruit set and then we can use the add method and let's say we want to add grape okay and actually we need to print this out so it's a print fruit set and we'll run it and down here you can see that grape has been added to the set if we want to remove something we can use the remove method so we could say fruit set dot remove and let's remove great okay so if we go ahead and run this now you'll see that there's no grape we removed it if we want to clear the set entirely we can do that as well so we can say fruit set and we want to do dot clear now if I try to print fruit set even though I cleared it it just gives us basically an empty set okay now you can delete it altogether which is different from clearing it out clearing it oh you still have the fruit set there's just nothing in it if you want to delete it with with del and then you try to print it out it's going to give you an error and say it's not defined so deleting it is the same as just never defining it alright so I think that's gonna be it for tuples and sets so let's move right along to dictionaries and dictionaries are there collections which are which are unordered they're changeable and indexed no oh that's one thing I forgot to show you I meant to show you this in sets no not sets yes sets because there's no duplicate members so I want I wanted to show you what happens if we were to add something that's already there sorry about that guys so I'm gonna go down here let's see how should it did this before all this let's say add duplicate so there's already apples right so we'll add apples and if we run that you'll see we don't get any kind of error or anything like that it just doesn't add apples twice okay it's already there it's not gonna add it twice okay so I just wanted to show you that before we moved on so a dictionary is very very similar to an object literal in JavaScript it's similar to a hash in Ruby you know every language they're all very similar than they have similar data structures but sometimes they're they're they're named differently or there's there's subtle differences but if you know like JavaScript objects and Jason it's they're very similar to that so let's create a dictionary so we'll say person I'm gonna open up some curly braces and then we have key value pairs now the keys should have quotes like that okay and then we're gonna put this as a string of John so first name we'll put a comma and then last name which we need quotes so last name doe and let's do age and age I'm gonna make an int so no quotes okay and if we go ahead and print and we can print person let's print the type as well okay and we'll go ahead and run this with Python three dictionaries dot pi so it gives us the dictionary and it gives us the class of dict all right so we can also use a constructor so to use a constructor we can say it's do person 2 equals dict and in here we can do first name this is a little different will do first name equals sarah class name equals Williams and if we go down here and we print the type and the value of person 2 you'll see that it prints out the dictionary and the class of dict I'm going to comment that one oh now if we want to access a single value or get a value like let's say we want to get the first name we can go ahead and print person now in JavaScript we would do dot name with an object literal in python with a dictionary we're gonna use brackets and say person name like that I'm sorry first name okay so let's go ahead and run that and we get John now there's another way to do that do this and that's using the get method so if we say print person dot get and then we can just pass in as a parameter the what we want to get which let's do the last name okay so if we go ahead and run that we get Doe so you can use either way this is the the more common way we can also add something so let's say add key value will take person and let's say we want to add a phone number so we'll say phone and we'll set that to a string look at there I go with a semicolon okay and then down here we'll go ahead and print person run that and notice that now there's a phone number added to this this dictionary another thing we can do is we can get all the keys if we want so let's say get dictionary keys and we could do that by saying person dot keys okay so let's go ahead and run that and what it does is it gives us this dict keys and then first name last name age and phone at the same time we can get the items so let's change this to items and we'll save that and it gives us this right here dict items and first name John last name Doe so that's how we can get items now I'm going to show you how we can copy a dictionary so I'm gonna creates a person - I don't have that up here right yeah I commented that out so I'm gonna say person - equals for the person dictionary with the copy method okay and this is similar to yes I know I keep bringing up JavaScript but again I know a lot of you guys are very familiar with JavaScript so this is kind of similar to how the spread operator works where you would use it to get all the values of an object and then if you wanted to add to it you could so what we're gonna do is take person to now which is a copy of person and let's add a city value to it so we'll say city equals Boston alright and then we'll go ahead and print person two and run this and now right here is where we want to look this is person two which is a copy of person 1 our person but also has the city of Boston okay so let's move on I'm going to show you how to remove an item so to do that we can use Dell I'll say Dell person and let's let's remove the age so we'll pass in age and then down here we'll go ahead and print person and let's run it and this last one here you can see there's no age another way we can do this is with pop so person dot pop and we can just pass in whatever the field we want to remove so let's say phone and now if we run this you'll notice that the age and the phone is gone let's see we can also clear okay just like we can with some of the other data structures we can do person dot clear and if I try to print person what we're gonna get is just an empty dictionary so just this this set of empty curly braces we can also get the length let's see we still have person too so let's do print and just like with the other structures we can use the Len function and then just pass in person to and let's see what we get so that gives us five all right so it gives us 5 because person 2 has 5 key value pairs now just like with JavaScript a lot of times you'll have an array of objects so we can also have a list of dictionaries so let's create people and set that to a list so we're going to create some square brackets here and then inside here we'll have a dictionary and let's just do name I'll say name Martha age 30 and then we'll put a comma and we'll put another one say name Kevin and age 25 okay so now we have a list of dictionaries I'm gonna show you later on how to how to loop through these and stuff but for now let's just go ahead and print this so we'll print people and there it is so it's just an array of dictionaries now if I wanted to get let's say the name of this first person here in this list I could say people 1 which is gonna choose this dictionary okay this item and then the specific field which I want which is name so that should give me Martha so we run that I'm sorry it's you me Kevin because Kevin is in the one position Martha is 0 all right so I think that's gonna do it for dictionaries let's clear this up and let's move on to functions so we're gonna open up functions pi now a function in Python it basically does the same thing as it does in most languages it's a block of code which runs when it's called now there's a big difference in the way we format functions then most C syntax languages ok we don't use curly brackets we use a colon and then we use indentation okay and that can be with tabs or spaces so let's go ahead and create a function so I'm just going to create a simple function called say hello that just takes in a name parameter and then just prints that out so to define a function we actually use the DEF keyword okay so we want to define say hello and instead of doing this like we do in many languages we put a colon and then we just want to indent one over from here okay and envious code and in any good text editor or it usually does this for you so let's go ahead and just print and I'm actually gonna take in a parameter here so let's say name and let's just do a print let's use an and we'll use an F string here so we'll say print hello name okay now this by itself isn't gonna do anything we just define the function we actually have to call it so we'll say say hello and then we have to pass in a name we'll just say John Doe alright so go ahead and save now I do have the prettier extension installed in vs code so it does kind of format it on save a little bit so that's if you see me save and things change a little bit that's why so let's run this we're gonna say Python 3 functions dot PI and we get hello John Doe alright now we can also do default arguments or parameters because if I were to do just say hello without anything in it we get an error it says missing one required positional argument but what we can do if we wanted to set a default we could say like let's say equal say let's same Sam so name equals Sam and if we run say hello now with no argument you'll see we'll get hello Sam okay so you can do that alright so usually you're gonna deal with return values okay when you run a function usually it's it's you get something from it you're not you almost never are gonna print something out like this unless it's point is to to be a logger or something like that so let's create a function called get some and get some will take in num1 num2 i'm sure you can guess what this is going to do it's going to let's see we could just return let's actually create a variable within the function scope called total we'll set that equal to num 1 plus num2 and then we're going to return total okay now when we set variables inside functions it's in this scope okay so outside of it is going to be the global scope this is the the function scope so this will return the total so we can go down here if I just do get some and pass in let's say three and four and they try running this we're not going to get any output because we didn't print print is what causes the output to the console so I could wrap this in print and run it and then we get seven a lot of times though you'll use the return value in some way and you'll assign that to a variable so let's say num equals get some of three and four and then we could print num run that we get seven so num is equal to seven because it's equal to the return value of that function alright so I want to move on here to what's called a lambda function so a lambda function is a small anonymous function it can take any number of arguments but can only have one expression and again I'm comparing this to JavaScript very similar to arrow functions okay so if you're familiar with es6 if you use react or anything like that I'm sure you've used arrow functions before this is pretty similar all right so let's take the to get some example up here and let's let's turn this into a lambda so we could just simply do get some equals so we're setting a variable just like in JavaScript we would do like Const get some I could even so get some equals and then we use the lambda keyword okay and then we want to put in our parameters so we have num1 and we have num2 all right and then we're going to put a colon here which is kind of like an arrow and then with a narrow function and then our expression which is going to are the body of the function which is going to be num1 plus num2 okay and it's gonna it's going to implicitly return whatever this expression equals and it's gonna put it into this variable so if I go ahead and I say print get some and let's pass in 10 and 3 so if I run this we should get 13 wait a minute oh you know what I think my prettier extension just turned this into it I just it added def and added the return I shouldn't need those though I shouldn't even need these parentheses yeah it turned it into a regular function let me try that again it got rid of the lambda and everything see sometimes this prettier extension doesn't do what I want yeah see I save it and it turns into that huh you know what let me disable that real quick oh that's not right so I'm gonna go to settings format on save let's set that to false all right so all right so now it's not I'm saving it and it's not redoing it for me so let me try this again and we get 13 all right so that's a lambda so we're gonna move on now to conditionals so 1 clear this up and let's open up I will save it let's open up conditionals dot Pi which is right here and we're gonna look at if statements if else statements and these these work pretty much like any other language you test to see if something's true or false and you you do something based on that condition so I'm just going to create a couple variables up here let's say X equals 10 y equals 5 and we when we do an statement we can use comparison operators like equals to not equals to greater than less than greater than or equals less than or equals so let's do an if statement here now we don't have to use parentheses like that like in a lot of languages you'll use this syntax we're just going to say if X is greater than Y and then we want to put a colon and then just indent the next line and I'm just going to do a a print will use an F string and I'm just gonna say X is greater than Y and obviously you can do whatever you want in here I'm just gonna print this out though okay so let's save this and let's run it so Python 3 conditionals dot PI and we get 10 is greater than 5 now if I were to change Y to 50 and we run it we're not going to get anything because this isn't running because this is not true now you can also have else okay so if we wanted something else to happen if this isn't true then we could do that let me just put a comment here so this is a simple if and then we'll just do let's say if else so I'll go ahead and just copy this and then let's put an else so we do else : and then just indent the next line and I'm gonna copy that print and just reverse it we'll say Y is greater than X okay so we'll go ahead and run this and we get 50 is greater than 10 okay it's running the else because this is not true so let's see let's come let's let's actually copy this if-else because now I want to show you how to use an LF or an else if it's actually a LIF you know IIF so let's say not only do we want to test to see if it's greater than or less than but also if it's equal to so in the middle here I'm going to put a LIF : and then we'll go ahead and print something so we'll print X is equal to Y okay so if I run this right now we'll wait a minute what'd I do wrong here no it's syntax oh I didn't put a condition so this Elif here obviously this needs a condition we're gonna say if X is equal to Y all right so if we run this now we're gonna get 50 is greater than 10 but if we change this to be equal like let's change Y to 10 as well and we run it now we get 10 is equal to 10 okay this right here this condition is true so it's running this now we can also do nested if statements which is an if within an F so for instance if I wanted to do if X is greater than 2 and then do another if statement here and say if X is let's say less than or equal to 10 then let's do a print we'll say X is greater than 2 and less than or equal to 10 so we can do that and right now it's equal to 10 so that should run wait a minute oh I forgot my indent okay so now it runs now this isn't a great way to do this if you wanted to do this exact condition what I would suggest doing is a logical operator and using and okay because what you're saying here is both of these need to be true right so what we could do is we could instead say if X is greater than 2 and X is less than or equal to 10 okay so it's a cleaner way of doing it and then we would run that okay so let's comment this out and run that and we get the same thing and you can also do or and not so if I were to copy this and do or the difference here is with and both of these have to be true for this to run with or just one of these has to be true one or the other so this would be or all right and then we also have not so for not let's just do something really easy I'll say if not and we can pass in here a condition like x equals y then oops actually we'll just type this out so print X all right and that shoe actually they are equal right now so I'll change that to let's say 20 and now that should run so you'll see right here 10 is not equal to 20 so in fact all three of these are running because they're all they all evaluate to true all right actually no they don't hold on oh yeah they do because we didn't even test why all right so I'm gonna comment this stuff out and let's move on to membership operator so basically what what this is used for a lot of times is to test to see if something is in like a list so if we do numbers and we set this to a list and let's say we want to test to see look we don't need that if we want to test to see if 3 is in the list I'll actually change the x value up here to 3 so let's say if X in the name of the list which is numbers then we could do something and we could even do this we could say print and we could do X in numbers just like we did in the if and what this will do is give us a true or false okay so if this is true then this this is going to give us true so if we were to run this you can see we get true at the same time we have not in okay so this is this is an in and we also have not in so we can say if X not in numbers then let's print X not in numbers right now that's not going to run because three is in the numbers but if I were to change it to let's say thirteen and run it we get true which is corresponding to this right here okay we also have identity operators of is and is not so for instance and I don't use this too much but we could just to show you it's possible we could do like if X is y and then we could do the same thing we did above by printing the conditional or that the we'll get a boolean from this condition print X sorry is why so let's actually comment this out and if I run this we get nothing because X is not Y but if we change it to 20 and we run it then it should give us true okay it gives us true because X is y and then at the same time you could do is not so we could say X is not y and then we'll print true if X is not Y so we'll change it to something else and we should get true again from that statement and that's that alright so that was a little longer than I wanted to spend on conditionals but yeah so it's it's pretty simple at least basic if if-else and stuff like that so now we're going to move on to loops okay loops are an important part of any language a loop is used for iterating over a sequence that is either a list a tuple a dictionary a set or a string or a custom a custom condition so let's do a simple for loop that loops over a dictionary so we're gonna say people equals I'm sorry not a dictionary a list so let's say John Paul Sarah and Susan alright so I just want to do a simple for loop so I could say for person it's actually a 4 in if you're familiar with es6 we have 4 ins in JavaScript es6 so we can say for person in people and let's go ahead and print and let's just put an F string in here we'll say current person and then we'll put in the variable person which represents whatever person in that in that current iteration so let's go ahead and run Python 3 loops pi and we get current person John it goes through again Paul Sarah Susan now we can also break out of a loop if we want so let's let's look at break so I'm actually going to copy this but I want to say here I'm going to use an if statement I'm gonna say if person is equal to let's say Sarah then I want to break otherwise I want to print this current person so let's see what happens here if I comment this out notice that we get just get John and Paul so what happened is we broke out of the loop we basically stopped it if the person was Sarah now we also have a continue so let's see what happens if we do that so I'm going to copy that and instead of saying break we're still going to test to see if it's Sarah but instead of break let's do a continue and let's comment this out so now we get John Paul and Susan so it didn't just stop the loop when it got to Sarah like it did with the break it basically just skipped Sarah and kept going and then called Susan okay so that's the difference between break and continue so we also have something called range okay so let me give you an example of that alright so I'm gonna say for I in range now we could put anything we want in here basically any range any numbers first I'm going to show you how to use it with the list we just created the people list so we can take the length of people okay so for I in the range of the length of the people list and then let's just print say people I okay so this is simple similar to just a standard for loop we're gonna go ahead and run this and it's just gonna print out all the all the people's name I could've did I was an F string current person or whatever and instead of just person I'd have to use people and then I and we could do custom ranges as well so if I wanted to do for don't want that for I in range and then we could put let's say 0 to 11 and then let's just print we'll print an F string we'll say number : and then we'll put in I okay we'll run that and it's gonna go as you can see whips it's gonna go from zero to ten all right so starts at zero goes to ten because we said zero it's not actually going to go to 11 it's not going to show the 11 it's going to go to the the number before that so we can also do while loops so while loops execute a set of statements as long as the condition is true so we could set a variable outside of the loop like count set it to zero we could say while count is let's say less than or equal to ten then let's go ahead and print and I'll say count count and then we just need to increment count by one so we can actually just say count we could do equals count plus 1 or the shorthand would be just plus equals 1 like that so let's try it out let's clear this and run it and we get count up to 10 okay because we said less than or equals to 10 if we just did less than it would bring us to 9 all right so that's loops next thing we're going to look at is modules okay so a module is basically a file containing a set of functions to include in your application you have core Python modules you also have modules that you can install with the PIP package manager and Jango is one of those as well as custom modules okay so you can create your own modules and I'm going to give you an example of all three of these so first thing I'm gonna do is I'm gonna show you how to import a core Python jool where you don't have to install it you don't have to do anything except import it an example of that would be the date/time module so to import a module we use the import keyword and let's say import date/time and I want to use this so I'm going to go down here and let's say we'll create a variable called today and let's set that to date/time dot date dot today okay and if you look at the documentation you'll see all the different methods and properties and stuff that are available so let's print today and let's see what we get so we're gonna say python three modules dot pi and that's what we get okay so today is eleven twenty eight twenty eighteen now notice that I did date time dot date dot today so this date object is actually in date time and if I wanted to I could actually import just date from day time okay instead of importing the whole thing the way I would do that is by saying import I'm sorry I'd say from date time I want to import just date okay now if I do that I can then do today equals date dot today okay so I don't have to use day time because I brought I imported in date from date time so let's save that and see we should get the same thing excuse me let's look at another one let's bring in time so we'll say import time and let's see let's go down here and let's create a variable called timestamp and set that to time and then we'd actually have to do dot time taught time stamp for that to work wait is that right no I'm sorry it's just time dot time like that and then let's go down here time stamp and what it does what that time stand our time method does is prints out the current time stamp so let's run this again and it's gonna change each time okay because the time stamp is obviously keeps changing now this looks kind of funny so what we could do is just import time just the time method from the time module so just like we did with the date time we could say from time import time and then we could simply go like that and that should do the same thing alright so those are the those are examples of just core modules that are available by default with Python now python has a package manager called pip and again comparing it to JavaScript where you have no js' you have your NPM package manager you know you have ruby gems a lot of different languages have different package managers for installing external modules or programs excuse me so to install something with pip you want to do pip install but since my Python 3 is available in my Python 3 command then I want to use pip 3 ok unless you set up what's called the virtual environment which we're not going to get into in this in this crash course we do do that in the the Django udemy course but let's go ahead and install something using pip or pip 3 in my case so this there's a very very small module called camelcase which just takes a piece of text and makes a camel case I mean capitalizes each word or whatever so let's do pip3 install camelcase now what this did actually it's already installed so that's why mine went so fast but when you when you run it like this it's installing it globally on your system now like I said you can install something you can create something called an in virtue of virtual environment where when you install something with PIP it gets just installed in that environment you can also use something called pip and for pip env which does the same thing you have these encapsulated environments in my case it just got installed globally kind of like doing npm install with a - - g or - - global now if i want to see what's installed I can say pip 3 freeze ok so this is going to show me all the modules that I have installed and since I'm in a global scope this is what I have installed globally and you can see camel cases right here alright but if I were in a virtual environment it would just show me what is in that environment so now that we have that installed we can import it just like we did with these other ones so I'm actually going to put a comment here so these are core modules and this is we'll say pip module so we can import camelcase it'll actually pop up here so in Port Campbell case and let's go down here and what we need to do is basically instantiate a camel case object so we'll say C equals actually no it will bring in camel case bring in the methods so I'll say from camel case we're gonna import a method which is called camel case and we want to make these uppercase alright so doing that we can just say C equals camelcase now this this object now has methods on it one of them is hump okay so we can say print C dot hump I know that sounds a little weird and let's pass in like hello there world all lowercase and let's run that and you can see that what it is it made every first character of each word uppercase okay so it's a very very simple module but it's just an example of how to install something with PIP and how to import it and use it so the last thing I want to do here is create a custom module and use that so we have this validator dot Pi file which is already created already filled out basically what this does is it validates an email okay and we imported the re the regular expression module which is a core module we created a function called validate email takes in an email and then checks the length of it and then it uses that regular expression module which has a match method and passes in a regular expression to validate an email okay and it returns a boolean or returns a true or false based on if that is an actual email or not so let's say we want to use this as a module so I'm going to go back to modules dot pi and we're going to bring this in so let's say imports custom module so say imports validator and actually you know what I mean we could do this and we could use validate or dot validate email but we could also do from validator import validate email it'll actually show us show us that okay now we can use this validate email function and we could have as many functions as we want in the validator if you wanted to have like I don't know validate username or something and even have it connect to a database and see if their username is already taken or something like that so down here let's have an email we'll set it to test at test comm actually it should be a string so it's a valid email and we're gonna just do if validate email pass in that email and then we'll do a print email is valid okay and then we'll do else print email is bad alright so let's get rid of this print here get rid of this one okay let's run it so we get email as valid if I change this to be like let's say test and we'll put in like a number sign here we get email as bad so it's using this validate email function it's bringing that in from our validator module which is a custom module that we created okay so that's how you can use custom modules alright so now we're going to move on to classes okay with Python you can do all types of different programming types you know you can do procedural you can also do object-oriented programming and a class is used to create objects okay an object has properties and methods methods are basically just functions that are associated with it almost everything in Python is an object and you can see when we have a string we can call we can call methods on it a string as an object and almost everything is an object so let's go ahead and create a class I'm gonna try to do this quick because we're really running out of time here so let's let's create a class called user and if you've created classes in PHP or Java C sharp and it's it's pretty similar so we can have a constructor so a constructor is basically a function that runs when you instantiate an object from a class and we want to define this as double underscore and knit double underscore and this is gonna take in self and it can take in other other properties as well like let's say this user we want to have a name and then inside here we can see we can assign self dot name equal to name now in a lot of languages and when you use a class you'll use this okay so in a pie in a standard Python class you're gonna use this self ok so just think of that as this if you're coming from like es6 or PHP or something so to create an object say we'll initialize user object we can do like let's say Brad losing my voice Brad equals user okay so we saying Brad is going to be a user object and we can pass in a name like that so just doing that will create the object so I mean if I save that and I run Python 3 classes hi we're not gonna see anything but it didn't stand she ate the object in fact they can do a print let's do print type Brad and you'll see that it gives us basically telling us that this is a user object now I'm gonna add a couple other properties here so let's do name email and age and then we just need to go in here and say self dot email equals the email that's passed in self dot age equals the age that's passed in and then we'll go down here we'll add that in so brad at gmail not my real email address by the way and then it's due 37 okay so we're just adding extra properties now let's create a method that is associated with this actually first before I do that I want to show you that we can actually access the properties so let's actually print let's print Brad dot name okay if we run that we get the name we can access any property we want Brad dot age all right now I want to create a method so to create a method it's just like you know any other function we're gonna use def let's call this greeting now these methods that we create within the class are going to take in self and we want to just return let's return an F string and we'll say my name is now when we want to access any of these properties from any method within the class we need to use that self keyword okay so what say self dot name and I am self dot age and then down here if we want to run that method we can simply take the Brad object and call greeting make sure you put parentheses because this is a it's a method it's not a property and if we run this what do they do I forgot my colon so if we run that we get my name is Brad traversée and I'm 37 okay if we wanted to do another method like let's say has birthday and what I want this to do is just add an extra year to my age so I'll say self dot age and we'll just do plus equals one so we'll add a number now if I go before the print before we run the greeting and actually I don't need to print we just need to take the Brad object and call has birthday once we do that it's going to add one to the age and then we'll per do the greeting so we start off with 37 have a birthday and then when we print the greeting it should be 38 and there we go excuse me I am 38 okay so I mean that's the the basics of creating a class with with methods and instantiating it and calling those methods you can also extend classes so let's say I mean we have a user class let's say we wanted to have a customer class and extend that user class okay so we'll go down here and we want to just create a class called customer and a lot of times in other languages like I'm sure a lot of you guys work with es6 and JavaScript you would do like extends user in Python we want to actually pass it in as a parameter like that okay and then let's basically copy this constructor so we'll put that here and I want I want a customer to be able to have all of these fields but also a balance and I want that balance to initially be set to zero so I'm gonna say self dot balance and let's set that to zero by default okay and then this customer class is going to have a method called set balance so let's say def set underscore balance and that's going to take in self and it's also going to take in a balance all right and then what we want to do is take self dot balance and we want to set that to the balance that's passed in okay so now let's go down here and let's in it let's initialize a customer so let's say janet and we'll set janet to customer and customer takes in the same things as a user because it extended it so we'll say janet johnson janet at yahoo.com we'll say 25 all right so we have janet who is a customer so we should be able to set a balance so let's say janet dot set balance and we'll set it to let's say 500 all right now I also want to have a greeting for the customer but I want the greeting to also have a balance in it so I want to overwrite this greeting so what I'm gonna do is copy this and paste that in and we just want to add right here to the end of this string we'll say my name is name I am age and my balance is self-taught balanced alright actually first of all I want to show you that we can still access parent class methods so if we don't even do if we don't even do that yet let's do Janet dot balance I'm sorry not balance greeting sorry guys this is a long-ass video so if I run that hold on wait a minute Janet oh I didn't print it you know I'm not even gonna bother editing that how guns I don't care okay so you'll see that Janet even though as a customer can still call greeting even if it's not defined in the customer class which is right here because customer extends user okay but if we want to overwrite that and have it do something else like have the balance in it we can do that so now if I run it we get my name is Janet Johnson I'm 25 and my balance is 500 alright so yeah that's that's pretty much it guys so you create your class you can add properties methods and you can call those properties and methods after you instantiate whatever that object is okay so let's move on to dealing with files okay so files dot PI so python has functions for creating reading updating and deleting files so I just want mean there's a lot you can do but I just want to basically show you how to how to create a file open it right to it stuff like that so to open a file we can create a variable let's call it my file we want to set it to open and then give it a name and this open will actually create it so I'm I call it my file dot Tia txt it's gonna be a text file and we want to write to it so we want the mode which is gonna be W okay for writing so let's save this we'll go down here and we'll run this so python three files dot pi and over here you'll notice that it created my file dot txt just this one line created a file on my system so we can get info on this file so we can print so let's do print name yeah we'll just do this so print name my file dot name okay so my file is basically an object that has properties on it that we can access so we can do name we can see if it's closed or not so let's say is closed and this has a property called closed and we also have a property called mode change that to opening mode all right so let's run this so gives us the name is closed as false opening mode is W and what it mean what I mean by closed is not the actual file closed on our system but if we closed it within within our script here so let's write to the file okay so I'll say right to file so we can take my file and we can call dot write and let's put in the string I love Python alright and then let's also do my file dot write because we can keep writing to it we can append to it let's say and javascript okay and then we want to close it so we're gonna say my file dot close so if we ran this is closed undoubted be true so let's save that and run it and let's go to the text file and there we go I love Python and JavaScript okay so let's say we want to F this has already been closed let's say we still want to append to it we still want to add to it so what we can do is we can then open it again so just like we did up here I'm gonna say equals open my file text only this time we're going to use a we want to append to it otherwise it's we're gonna overwrite it we don't want to do that so go ahead and paste this in let's put I also like PHP and then we'll go ahead and close it okay so we'll run that again let's take a look I love Python in JavaScript I also like PHP so it's as easy as that and if we want to read from a file we want to open it again this time we want to use the we want to use our plus as our mode and let's create a variable called text set it to my file dot read let's read one hundred characters and let's print it okay so we'll go ahead and run that and there we go I love Python and JavaScript I also like PHP so that's how that's starting to work with files obviously there's a lot more you can do but we're gonna move on now to working with Jason okay so jason is commonly used with data api's here's how we can parse a jason into a python dictionary so a lot of times you might be dealing with third-party api's where you're dealing with data that comes in is Jason and you're gonna want to be able to parse Jason into a Python dictionary so you can work with it you'll also probably want to parse a dictionary as Jason so there is a module called Jason that we can use so we want to import Jason and I'm gonna just create some sample jason like we can pretend we're getting this from some outside api or something so let's say user jason equals and it's gonna be a string of jason which has double double quotes around the key in value so let's say first name john last name doe and age that's a number so we can do 30 all right now we want to be able to pass this to a dictionary okay just like you know we have jason dot stringify and jason dot parse and javascript we have methods like that in python so let's say user equals jason and we want to do jason dot loads and then user jason okay so then we'll go ahead and print user and then down here we want to run Python and the name of this file is PI underscore Jason dot pi and the reason I unexpected indent oh ok so it gives us the dictionary of the user now the reason I called this pi underscore Jason and not Jason PI is if I use Jason PI we get a conflict because that's the name of the module in case you're wondering that all right so let's say we wanted to just get just the first name we could do print let's do print actually we'll move this down here let's do print user first name and such it's a dictionary we should be able to do that so let's run that and you can see we get John alright now I'm going to show you how to do the opposite and take a dictionary and turn it into JSON format so let's say we have car which is gonna be a dictionary so make we'll say Ford and let's say model Mustang and let's say year 1970 so that's a Python dictionary right now we can say car Jason will create a variable and then we can use that JSON module and we can say dot dumps and pass in car okay so this will do the opposite so if I go ahead and print car Jason let's comment out these prints and let's run that and now you'll see that it's in JSON format we have the double quotes alright guys so that's gonna be it for this crash course I hope you enjoyed it I know it was very very long but I wanted to cover a wide range of just core concepts that you're going to need to know to do anything in Python and and I know that it's kind of difficult to see how a lot of this stuff is useful like how can you actually create something from it but it's all needed if you look at any Python script you're gonna see dictionaries functions conditionals lists you're gonna see all this stuff so what I would suggest next is to move on to tutorials or books or courses that are going to actually show you how to put it all together and build a project with it but again these crash courses these are always gonna be the very first step to take so that's it guys please leave a like if you liked the video also if you want to check out the django course that this is based off of i'll leave a link in the description with a promo code for just $9.99 alright that's it thanks guys and I'll see you next time

Channel: Traversy Media

Views: 426,063

Rating: 4.9675555 out of 5

Keywords: python, python programming, python crash course, learn python, python tutorial, python3

Id: JJmcL1N2KQs

Length: 95min 46sec (5746 seconds)

Published: Wed Nov 28 2018