How to Create Login System using Python | Python Programming Tutorial | Edureka Rewind

welcome on behalf of Eda I've been in IT industry close to 20 years and I'm an Al of Mumbai University so as you know the topic today is python logging system and I'll cover the different faets or aspects of python loging system so here's an agenda quick agenda what is python I'm sure a lot of you there uh would know what is python the python features login system and prayer requisites objectives so you will see a demo of it as well all right so here's the plan out of this session first I'll go through some theory in this deck after this I'll show a quick demo of how the login screen will look before I actually delve into the code part right so what is python it's a scripting programming language and I'm sure everybody would know it's one of the most popular languages programming languages scrip language out there just a small fact it is I know some of these things are not very important from the technical but it's it's a good ice breaker a good thing warm up by having this kind of slides I am not sure whether you know the origin of this name python so it was based on some comedy troop called Monty Python it's not the python the snake that you see on most of the cover pages of in fact all the books right so it's not the snake it's actually based on comedy group so it's a light Fact one of the best things about python is it's the syntax and everything is easy I'm sure most of you would have seen python code so see any any programming language reading and writing takes different effort right reading is always easier even if you learn a new language whether programming or our own language reading is always easier the writing is always complex the one best thing about python is even if you don't know python much if you read a python you will understand a lot of things it's very int intuitive and that is what it means easy syntax to write yeah you need some practice but to read it's quite simple so feature of python so Simplicity like I said it's very simple to understand so there are a lot of libraries lot of features on top of it but the core it's very easy to understand very intuitive and once you have some practice you'll find you prefer it compared a lot of traditional languages programming language out there and for writing code it's an open source so yeah you can install out there for everyone and you can uh use it for commercially as well and there are package managers Library such as anakonda I'll come to that portability uh yeah you can run it anywhere you have a python virtual environment or a python interpreter you install it somewhere you can Port your program even between Windows machine and Linux machine it's very easy to Port without much hassle so one of the most important feature of python is extens ability right so what it means is you can see one of the things with scripting languages since it iset I mean especially language likeon is interpreted that is some delay in um executing so it's not like you are compiling a code so any compiled code will have a better run for performance for example if you write something in cc++ and compile it it will definitely have a much higher performance as compared to just writing python so one of the best things about python is you can extend it by adding C library so there's something called syon so what syon is is you can actually Define the variables in Python using some commands like CDF and then what happens is you can then compile it into a c program it becomes a c program but that c program you can directly import into the Python program just like and you would import any other Python program what and these three programs are super fast so basically if you write a just to try your computer write a for for logic iteration one million times write a python and you write a syon and then import that python you'll see drastic improvement in performance when you run and see so that that extensibility is one of the uh good features of Pon along with that there's so many libraries out there for python which can be imported so that's I'll that in a moment so it's an interpreted language all right so yeah if you write syon you can compile it as a c code but essentially it's an interpreted so there's an interpreter which looks at line by line each line of python and then executes and that there's an error it will stop there so it's an interpreted language and that makes it very easy to debug python programs advantages Library so this is I mean there are a lot of important features of python but I would say this is number one because there's a huge open source Community working on python who supports different kinds of libraries so anything from socket programming to machine learning deep learning even Quantum Computing so any new technology comes up there will always be a python apis or support for Python and while there will be in each space you will have another language competing with python but you'll see python everywhere and that is parly due to the huge open source Community who like Python and any new algorithm out there for example machine learning and deep learning any new La algorithm comes out first you will see a python Library made out of it before you see other technology so that's one great and that's the reason we all want to go python or work on python most of the Technologies because that will be a li it's not a silver bullet right you can't use it every place but essentially a lot of new areas like deep learning machine learning cloud computing if you're working with AWS they have a goto library or if it's content Computing python helps a lot the last part is it's you can write it as a procedural language or you can write it as a object oriented so supports both flavors all right who uses python yeah so that's a a question that just answered a moment ago across different application they'll find uh you are users of python and just of different organizations and companies using that so now what is the login system it takes inputs from users right this is a login screen you enter an email ID user ID password you login and then uh if you don't have an account you sign up this is all login system is and there a few fa aspects of it which I'll explain as we move to the demo part so PR requests for login system right so what are the different blocks that comprise a login system so you have a login form that you just saw a moment ago then registration form for signing up and uh why I'm rushing through some of the slides is because you all could be familiar with what a log SC what is sign up because so everything every application nowadays requires some kind of sign up and login so that the third part is where the database integration for login authentication yes uh that's where all this information all the user records are stor and the HTTP methods to access I'll come to that so login system project objective we will be using flask framework right so those of you are not aware it's a micro framework build python web applications and it also comes with a lightweight web app server web server and that you can I plus get is embedded with a like with uh web server and uh you can actually host web application on using flask framework so one thing what flas is see it's very lightweight it's very easy to understand but and it's also very extensible which means the footprint of a flask framework is very light what I mean is very small amount of code will be there in a flask framework but you can add lot of other libraries like security or database on top of it and make it complete framework with all the features of a framework and the compartive to flask in the space is jangle so Jango and floss these are the top two uh web Frameworks we server and which host lightweight web servers for hosting web applications in Python then database integration there are multiple libraries multiple connectors you can use flas myb you can use anything and the URL the the web page right when you say URL the web page that you saw on the browser communicates with the web server the flask based web server WR in Python using post and get methods uh just hold on to this and when you see the demo and when you see the code this point will get much more clear right so login authentication what all entails in a login authentication so you read the input from the login form again database connection so database connection is basically to authenticate the users authenticate of the rise uh send those values to database and you will see all this in the demo as well as in the code so this is sign up me sign up reading again the same flow uh there isn't much different and you all know a sign up us but uh you know this is the same same standard steps except that you will be inserting into the database when you log in you're reading from the database when you are signing up you are actually uh writing into the database right so now let me show you a simple demo screen right so here's the thing okay so far I showed you a thetical presentation a deck now we as human beings we understand better by visualization than just text right so let me just give a glimpse of what we will be building and then before we jump into the code so here is the login sign up uh screen right and uh I'll just uh put CR7 let me enter credentials so it's saying welcome Cristiano Ronaldo because that's already there in the database right so let me R out let me say some other user I put an invalid password this incorrect password messy so here's the thing see usually in in Enterprise applications and all the whole login screen using different technology like mostly JavaScript based angular or reacts those kind of Technologies but this is how we build a login screen from python so this session is about that and one thing I want to just mention is usually you will not see this kind of error message invalid password for a user ID because the thing is due to security whether the user ID is incorrect or the password is incorrect you will get a generic message saying hey user ID or password is in so that you don't tell the person who's logging in hey there's already a user ID for this because this is useful for people who want to do some Mischief if they know there's a user ID existing they can do it also just for demonstration I'm showing the incorrect password but usually you will get a message that whether it's user ID part will say invalid all right example if I put something it will say invalid user now let me put the correct password for Messi and it will say welcome Messi so this is the profile page all right so understand this what you see here I just remember it notebook you note down this is the profile screen right when I'm saying hey welcome and then I'm showing a logout screen I click on log out it comes back to login screen right this is another HTML login let's say I try to add 20 Pro so so these are different football players if you don't know them so invalid User it's saying right so let me register let say CL let me enter this email ID and then I'll set up some password that's it so sign up successful you can go back to login screen now let me log in right so it's saying welcome to any right so you have a profile page you have a login page and you have a new page sign up all right so this is what you'll be going to see in the in the IND code so now what what do you see here on the left let me show you here so you can ignore first part so there's a login HTML right which is essentially HTML page so like me just open it and see how it looks I know all of you have seen HTML but uh just let me one with chrome so this is the pure HTML on Chrome now you'll see what is this Gibb don't worry I'll come to that but first of the uh objects on the screen you know same thing that you have seen here okay so that's all HTML is and there are three main htmls here login like I said this one login screen then the profile where it says Hey welcome you know Leon Messi and the sign up right new registration that I registered 20 okay so I don't want you to I'll walk you through some of this code but I don't you know want to build it as we walk along because this is something uh you'll get uh so this application I have bu for this particular session and uh you can making this HTML is not a big deal but I'll focus on the python part of it all right so so I want just want to show the flask okay I'm using the flask micro framework here so this is a rough copy what I me to say let me just show you flask before we jump in a login part of the screen okay so this is all again uh boiler plate code what I mean is you have a flask Library you import the the class from it and then you define the app so in this case name is actually will be main so you know any new program when you execute it will be main right so I'm this is a standard code so here is where you will find you know how easy it is to run flask okay so what you see here is something called decorators in Python okay so decorators are kind of a wrappers around functions so you have defined a function here and you just feed it to The Decorator right and the The Decorator will actually make it an endpoint or a the URL so this is a URL that you see and you want to map this URL to a specific function on the web server so this kind mapping is done by The Decorator takes of linking that URL with the function so what I mean is if I put a slash it'll say hey WR hello right so I'm just showing this code to know before you see uh this code and it Bec complicated let me show you the the smaller code right so I'm just saying uh hello all right so here's the thing uh let me just run this and probably you'll be able to see it right so that's it I just run this program and you see Z so Local Host so this is binding to some IP address 0 but I'll see something on local Port 51 okay so let me see 51 what do I have hello right on this on the screen so what has happened is I have said the URL is you know slash that's it it goes to this function right the browser sends um reaction to this particular uh function and it returns return hello all that's it and that's what you are seeing here let's yeah that's all so now let's say I want to build something so let's say I will just uh right so I don't have a welcome page so not font this URL is not there right so I just come right so I have started I change the code automatically the server has started so you can see below right so if you see let me use then so you see every time I make some change to the code this restarts here and then if I go and then now I restart welcome right so it's as simple as that so that's the beauty of FL 10 lines you already fired up a server okay and uh the last part so you can have you know another something else in of welcome and that you can put whatever you want and that's it it's all done and this is just saying from the application a certain you don't worry about all the are Boiler code but just boiler plate code but what saying is bind to this particular IP address which means uh you can connect it from local host or any other there's a public IP to This Server then you can connect to that so that's the part of about it right so that's about flask now let me show you the different artif effects right so let me quickly run through the HTML because this is more of a python web server or a login system so let me I'll focus on the python side let me just quickly show you some of the control field so I have a user field HTML so you don't have no HTML I'm just highlighting uh certain parts of it which so if you see there is a user right which you saw on the screen this user is there then there's a password right which is again you see password and that's it and then I enter this so what happens is so let me switch back to my so when I hit enter on this particular web page right login or something what happens there is an action right this is inside a form object HTML it's an action which says SL login right so when you hit enter on HML screen it it's the action is to call uh endpoint slash login and that slash login I have defined in my main program right SL login it's a big code so I don't want uh confuse you at this point of time okay so let me uh go step by step but that's what happens it comes to the login screen right now one thing uh I'll cover each aspects of flask right and how each each of this function helps you in defining or firing up the web server or serving the URL and end of the day we enter user we enter password we click login it'll come to this particular method and then what happens is what we will see right now before that let me show you this right so so what I showed you earlier was a rough one a simple 16 line Cod so that you can understand how simple flask is now I come to the main code initial Parts initial it's all same right instead of app I'm saying Main and blueprint is nothing just like an application so each application can be one so if you have multiple application there could be multiple blueprints so you don't to worry about all that it's just that simplistically main is an app that's why I say main. route if if I put slash on the browser it should take me to the index and what is the index doing there's something called redirect right redirect means you have to if there is nothing happening on the screen it should redirect to the main. login right so redirect URL for main. login main is this name of the program okay so redirect main. login main is the name of the application and login is the name of the function here right so what happens if I go back to the browser and I will not put any logins anything I'll just put slash that's it it still gets automatically redirected uh to the login right in case let's say I have put something else right return let's say I heard return render template I'll tell you what render template is for a sign up. HTML right and I'll comment this out so now what I'm saying if I hit slash right it should go and render so render is a technical ter is like rendering a template or rendering a HTML on the browser so if it's a slash don't redirect the login just show me sign up. HTML right let me try that again see now it's not taking me to login now it is to bring me to a signup screen okay so just it's like one line you can move here and there so that's some of the things flask makes your life easy on the respect let me restore the world to its normal order right so yeah it goes to talk right that's it so now let's move on to the uh the next part of it all right so for now uh let me just create a copy of it or let me create in the folder itself I have a copy this main uh let me just remove it everything is what is there come to that later okay so now what login happen when when I do login this is what is happening I'm setting under template login. HTML that's why when I say login or whatever it is whatever it is coming to this particular page right similarly new right new is the name that I have give for a sign up all right so if that is sign up request let's say I say new all right so what will happen if it's new I will render this HTML page on the browser I'm I'm basically uh returning this particular template or HTML to the main screen right so I'll say new comes a register screen right similar L there a third screen that I said right profile now you are saying render template profile HTML so let me say profile and some user all right let me just say profile saying not found right so now let's say I say see right so see name full name and all is not that because it's expecting uh full name right I'll say full name equal to you know and now let me run it so uh takes a while for sometimes I'm saying welcome L mess right so basically if I don't have any code I just say render render render I'll see those pages okay but uh that is so log out I'll cover later okay because once we complete everything else we'll move on to the log out part so let's go uh one by one right so when we are logging in okay here I have put something called right so for now you can ignore it I'll show it towards the end there's something called template Ginger templates on HTML screens for dynamic rendering of we pages so I know what I just said but it sounds very abstract hence you don't worry about error for now you just see Rend render template understand that a render template is to render a specific HTML onto the browser and redirect is to direct it to some function right so I'm redirecting to this function and this will do the Rend R okay uh that's about it now there's one other thing I I want to touch upon right uh called session okay so what happens is when you login to a screen so your user your some of your details are actually stored in session variables or cookies so that's why you know any application you go you go to multiple Pages it recognize it is you it doesn't ask you to enter your password at every every every step right so it holds some session information so that's something once you log in it is able to the application will tell you hey you are the so and so person so it will show all the different pages in the web application that is why earlier when I typed in Tony ton Cruz and logged it saying welcome ton Cruz because the session variable is a session is a variable which still stores Tony Cruz and then until I say log out it will not clear the session variable okay and now nothing will happen because it's all I'm still running with the older code so I just remove a lot of code but I'm just saying that takes you out okay the whole session the whole session information is removed all right so let me now talk about one other aspect in this main do route so like I said this is um this is a decorator decorator function right this this works on this function so it's wrap around the function so one is the URL other is the methods okay so I'm not sure you know how many of you understand the post and they get HTTP methods but let me talk about that a little bit so when we send a request from the front end to the server so either we do a get that means I want to see some request from database so I I sent a get request so I get me some details on the screen the other is the post where I'm submitting a form I'm submitting some details so it's a post and then it gets updated into the database variable so that is the post part of it and that's another aspect that gives depending on it's a post or uh get we can do uh different things okay now let me not write some code around it so let's say it's a login okay now when we log in what what should happen so if you go to the login HTML right it says login and Method post so I'm submitting the username and the password all right so I will go to Main and I will just say uh if request request is one of the um the methods are class classes within the flask library right so when you submit certain information from the HTML page you can find it under request all right so this is a object which holds uh all this the different information that is sent from the browser so if you say method is equal to post because I'm saying it's a post request right so I'm saying if request is equal to uh post let me take down those requests right let's say user is equal to user is a local variable so I'll say request dot request. form that's that's the so from so I'm submitting a form here let me go to login HTML so I'm submitting a form right hence uh you'll say request. form and then you will have user okay and then I will take the password right same same syntax request. form so what is let me look at the password name so if you see uh let me yeah user is uh name is user and uh password is uh yeah PSW right just about hello PSW so let me itas yeah so PSW so this is the password field all right and then uh see here's the thing now fine the user has entered user and password but how do we know whether the user is existing or not for that we need database right otherwise how will the program know and that is where I'm just introduced you to this particular mySQL rdbms database that's what I'm using here okay you can use any kind of database for holding this information but my is commmon uh it's also an open source and uh it's pretty powerful so I'm using mySQL database on AWS Cloud so this is not hosted locally I will hosted in on the AWS cloud and I'll show you how the table looks because now that you have entered the user and the password someone has to go and verify in the database right so how do you do that so that's where we have this let me open that specific show Ed so model.py all right so one thing is uh just in the interest of the time and the depth of the subject I'll focus on the CL flask web server but I'll just quickly run you through what this my model program does is it has a MySQL API right and there are some I'm giving four details right if I want to connect to a database I need four details one is the IP address so this is the IP address or in this case it's called DNS yeah domain name system DNS of the uh mySQL database on AWS Cloud database is Dev user ID is admin and password if you see it's a big brish I'll tell you why it's long vibration a moment but let me show you the table right so this is a MySQL workbench this is also an open source Tool uh you can use to connect to mySQL database on your local or anywhere in the world as long as it's you can connect it as a public DNS all right so this is the name of my table user and if you see I have four records already created right CR7 Kan K man and Messi and the so this is how I check whether the user is existing in this table or not so I'll just check username is the primary key I believe you know I mean I'm sure all of you know what is a primary key so there's a primary key and based on that I check the record is existing if it's not existing I have to insert a row right that is how sign up happens and if you see the password it's all gibberish reason being I'm actually hashing it it's never a good idea to save passwords the true password in programs or in database hence I'm using something called hashing what is hashing yeah that's again a separate uh topic but uh just not for now that whenever you send information in a secure website right your your your passwords either get encrypted or it get hashed right there are two ways uh so encryption means you encrypt something you can decrypt using same key somewhere else in case of hashing it's there is no unhinged hash you cannot extract the password out from a hash it's just like every time you know enter a new you enter a password the program will apply hashing algorithm on that and then it will go and check the hash value and then it will say is matching or not but nobody can know looking the database or the program saying hey what's the password entered no way because it's all hashed all right the other form is encryption but with encryption you can also decrypt using a key okay so basically that is that that is what hashing the difference between hashing and encryption is right so I'll just walk you through some of this I'm connecting there's a host host user password so what I'm doing here is uh instead of uh hash I'm using a encryption decryption here so I have this is an encrypted value of the password Crypt do decrypt will decode it right decrypt is a decoding function and I will not touch upon those uh topics here just so that not to confuse but cryp is another program that I had written to encrypt and decrypt so there are encrypt function decrypt function hash function etc etc but not to worry just know that there is a function which the password and then in this model model model. py is the one that interacts with mySQL that is why it has a MySQL connector imported right and it has a cryptographic module also imported so this connection is established and there are few methods this is get row get row is saying hey select St from user our username is equal to this so this is what the login screen does right it has to go and query the table and say hey select me a details username and it'll execute so this is all syntactical okay you don't have to worry much see one thing about is syntax a lot of this open source Technologies you will find the syntax everything on web online it's all out there so you don't have to worry too much about the syntax you will find that just about understanding what all libraries are there what all functions are there what all features are there so that you can execute it you don't have to by hard anything so this is the query cursor execute is saying just execute right and cursor is again you know I have a connection variable here so I'm connecting to my SQL cursor is uh another handle from the from the connection and I'm executing that handle here executing the query and I get the row and I'm reading the row so this is just getting the row for me next one is something called user exist now I'm asking this program this function hey does the user exist or not and then the same thing it does it says model do get row it calls this function and then it's saying if the row count is one cool at least the row is existing so it is taking the DB password right what is the DB password so I entered Messi right and and and it's it show it told me hey welcome message because it was able to identify message from the database so here it's saying hey database password is equal to something that something is coming from my SQL table this is that something right for the Messi this is the password and that gets R trade here and then what this program is checking is whatever is fetched from the database all the gibberish and whatever I have entered on the screen I'm hashing that I'm hashing that password generating a gibbish hashed it's not a giberish actually I'm just saying for simplity but it's a hashed password and I'm comparing it to Hash password and if it's perfectly matching I'm saying returning zero zero means all is perfect all is well I'm returning one when the user is existing but the password is invalid right user is that but password I have put and I'm returning to when the user itself does not exist all right so that is what the model is doing here and the user exist so just remember user exist is a function which says gets data from our database validates the password and returns get full name well it as the name s just it's getting a full name so full name is a is here you can see highlight it full name right so full name is there it just fetches the full name that's it there's not much into it and then the last part is me erase this marker the last is add user so where would add user be useful of course for sign up so I'm taking email ID username password full name everything I'm applying again hashing algorithm on the password that's all I I have to do after that I'm inserting it query this is standard SQL okay again like I said don't pret about the syntax and all it's all can find online it's not a you don't to mug up that mug up syntax it's inserting into the table user with all the values and then it's executing the query and that's committing that's it SQL commit that's it and then uh you have everything you need in the model.py and that is the reason I have in the main I have imported from model I importing main function model and from cryp typographic I'm importing the main function cry and I'm using those two so what I showed you just a moment this model model program all right just remember this is the handle we are using for a logging in okay so I have taken the password right now let's say I save this okay I save this and now I will go to login let's say what happens sorry it's no Lo and login it's login right let's say I say uh CR7 then I say CR7 Bri nothing happens right so I have a record and nothing happens that's because I removed the code right I deleted I'm not doing anything it's just saying render template it's not taking me to the profile page earlier what was happening was taking to my profile P saying hey welcome Christian Ronaldo but not now because I have removed the code so let me add that code but first I have to know whether this user ID and password is valid right I say let's define some variable and this standard variable can you and then model is the program that I mentioned which contains the database calls and user yeah user exist I'm going to Ty but because I imported I can see a drop down I click on it user exists and I pass the two parameter user and password so so you can break your programs functions small small pieces right always so you don't have to worry about writing in one big code everything so this it makes your life easy shooting so user valid is a variable which contains three values 0 1 and two right so I said uh Zer means all all is well one is invalid password two is well the user does not exist so I'm checking that if user so one thing so all the IDS one good thing about all these IDs is the variables pop up even if that part of it and you all know that already but I'm just mentioning it here okay uh so I will just say return and I want to redirect it to the so this is see here's the thing all right I can directly render the page which is the profile page right I can directly render the profile page or I already have a profile function here which renders the profile page so let me just redirect to this particular function that makes my life easy right so whatever I do in that particular function this function will not get impacted I can change that function only here I'm just redirecting and I'm saying main is the name of main. profile so that's all what I'm going to do and uh there's one more thing so profile I also need a username right because like I said earlier if it's Messi it should say Le Messi or the user name you have to pass right that's how it is able to render and let's pass that username in this uh redirect right so main do profile and I will say user is equal to user so this is what that's it all right so that's all uh you have for if the user is perfect or the user is existing database the next thing is if I user is not let's say the password is invalid okay in that case I just user is invalid let's say invalid so the third scenario is the user does not even exist right this here uh we'll say us is invalid because user does not exist here password is incorrect for user okay so we we just want to add that so let me rected it's a post function then I have request. form a password user valid I'm checking if yeah user is existing I'm passing to the profile page here I'm saying password is incorrect and last part is user is invalid when it isn't existing in the database right so that's all it is and then I'm entering the uh login page so if let's say uh the request is not post some other request it will it will continue to stay on the login page however the request is a post and user is valid it will redirect to the profile page okay let's run this let me restart it's saying I G to the profile let me go to login so I will go to the initial login screen right so I'll say messy and I will enter let's may put a valid password login see now it has so ear it was not going in now it's going to the profile page right because I am redirecting to the profile page if the user is valid so one thing is I entered just Messi but how does it know Leon Messi that's because it's fetching the full name actually I hardcoded here but uh in this case let me remove it right so I just hardcoded because uh to De demonstrate but we can actually enhance this prefix page so we have to update so let me not put that let me just go back log out okay and let me enter Messi again and we'll see what happens I say Messi and I'll will say yeah so full name is not defined right there's no full name that means the profile function it's not complete I need to get the full name then only I can hand display it right so let me do this I will full name is equal to so we saw right there was a function in model extract full name get full name right okay get full name fine model. get full name it gives me this and then what do I have to pass I have to pass obviously the user since that is a key okay now I'm rendering the template profile. HTML F name is equal to full name I'm passing full name but what is f name well let's go to file HTML I will look at the let me Scroll once so that you can see F name somewhere here profile yeah so as you see uh let me highlight it fnn so it's saying welcome F name right and that is what full name getting pass here okay so now you wonder what all this open braces and all I'll come to that in a moment right so now I go to main I have set the full name full name is equal to model get full name passing the parameter now let me restart the server or server gets Auto restart every time I change the program okay so here what I'm doing is I'm just ping some data with a valid password and saying welcome all youy and just so that you don't I think there is some kind of trick here put har Kane right password is incorrect for Kan all right Kane is existing but I put an invalid password for it saying welcome Harry Kane why because Harry kanane is there in the database Harry Kane full name right as you see here second row so we have basically constructed the from login to the profile page okay now let's quickly go to the sign up or sign up page right so what happens when I say new it takes me to the signup page right now let me build so this is where it comes right now nothing is happening right if I say sign register let me fill something something nothing is happening because I don't have any program here right I haven't put any code now I have to do I have to add a user moment that is a sign up request right I have to add a user so that's what the new function will do okay so the first thing that we need to do is yeah we are checking if the uh see again when you go to the signup page when you go from login screen to the sign up page you are just showing an empty screen but once you enter the details and submit and then you click on register it's a post HTTP method right post so you're entering submitting data to the Spen server right so let's put it as host right so if um so what is that request. method the same code that we had earlier right so we are just we're looking at the request variable we're posting it and now here's the thing we we have to get the details so all the four details that we are going to fill because if right now if I say hry hry is hry existing H is not existing I'll say entry Sol there in the cach so I'll say the hry and nothing happened why because I Haven I haven't written full code so here's the thing I'll say now let me put that code request. form right user password is equal to request. form uh PSW sorry password and uh email is equal to request. form email and the last part is what full name full so this can be any name okay local variables but one in the square bracket should be coming from HTML yeah so that's what I did now what I'm going to do next is I have to insert this right so so I'll say model do add user that was the function right so in that add user we'll have to pass multiple variables let's let me use the AR uh star AR can email so what order I'm expecting the model add user okay email ID user password and full name all right email ID user password and uhor full name so I'm passing the and let me get some it returns from status right so anything anytime we add anything we need to check for the status here there are two statuses if the insert is successful I'll get zero if there is an error I'll get two and if the user is already existing then I'll get it return one right so zero means everything is cool right let me just say status status is equal to model the St the SQL code basically yeah that's the term uh let's call it SQL code be better otherwise it can mean something else right SQL code is equal to zero so everything is perfect okay when everything is perfect now you'll think what am I adding now flash okay flash is another way another Library within flask to show messages on the HTML okay it's as simple as that you just have flash you put some messages inside it and you are good to go and you can say use yeah sign up you can just sign up successful yeah go back to login screen because we have to direct that that is one thing then I have FF SQL code is equal to one when SQL code is equal to one and we are saying what is one one one means the user is existing is user is existing okay and um only thing is we'll just say user is existing usern name we have the username if and uh this is another good thing about all these IDs it will tell you if there's an error right right away flash if the user is not existing yeah some or insert failed it could be anything server not available right server issue I can put something of that sort and that's it so now let me run this program sign up okay refresh so this time when I enter some okay so render template sign up HTML there is some syntax ER return template sign up. HTML right so I have to add something here uh what is it saying so that is an issue just troublesho it quickly sign up successful skill code is model. add user user isal to user password sign up. HTML okay and this is sign up. HTML okay and let me just it should not matter but maybe didn't get refreshed okay so indentation problem it's say SQL code else LF SQL code right so let me see okay sorry I did some indentation problem so that's something you to be careful with python right I just put some space additional by mistake and through eror okay but again that's fine all the IDS will show all those errors so that's really nice of it so let me now try to register Jer Andre and uh let me the password right so user is already existing why because I have already registered the in the past right saying so let me try I'm just executing the query here in the database so this is a MySQL workbench so this is a good way to know what all values are exist so Henry is already there okay so we are short of players okay roon is not there let me put uh say okay that the cash p and that's it password yeah sign up sucessful go back to thing go back to L and then Rooney and that's it so welcome V Rooney so basically what we have seen is um most important login screen and what it does you saw it takes input and checks validates and returns message accordingly then you have um the new which is sign up just now we saw so you saw this sign up successful message at the top which gets flashed and then the profile page where it says welcome so these three we have seen we haven't seen log out but uh I think so here's the thing okay I have introduced uh during while I was working walking you through the code I didn't introduce a session variable uh just so that I didn't want to make things complex session variable is where we have to hold some values of the user or at the client side or maybe a server side but usually there are multiple ways but we to the clientel client side session information and then you want to log out we have to remove it from the session variable so just let me not make it more complex because it's not entirely uh relevant this part but just know for that and uh one last part that I want to show you is we are actually making this uh there's an init program right this initialization program which actually calls the main program so I showed you main program but uh init program is the driver this is where the entry point is so you'll see from flask same command except that there's one app. secret key that you give when you start an application so what happens is when you send session information to the client side you need to encrypt it and code it so FL takes care of that that's why you give a secret key at the start the session information is all encrypted and then you are importing the main function that I showed you all along then you're registering the blueprint blueprint is like I said an app within main that's it so this is again a boiler plate code uh you don't have to worry about the standard code here is where main is where I walked you through the various the you know the manuvering across various screens you can control through through main.py okay and uh just to reiterate quickly uh what we have done so far or what are the important components of this login screen like I saidit is initialization where the control comes here and this function create uncore app is a executed when you start the server and within that create you're setting a secret key you are importing the main and you are registering the app called Main and once that happens main starts executing and Main has different routes different URLs end points which will serve the different actions on the uh the UI side right the browser side and there are couple of other modules model.py it adds user it gets full name it checks users all that that stuff and there is one cryptography module uh which is this again added in just for this for encrypting decrypting the password that is entered right so there are two passwords here right one is the database password other is the password that I enter as a user so as a user I can enter any password hence I'll hash it and store it in the database as a hashed value the database password I'm only I know obviously I I should know and since I should not expose it and in the open in the public so that's why I have the encrypted password and then I'm decrypting it while I'm connecting so and for decrypting encrypting there is something called um some keys so I'm using specific key so which I mean you can see key and you can encrypt different matter but I'm just saying time application you will have this kind of encryption and encryption right then hashing so so these are the different uh modules you don't have to worry too much about model and cryptography this is where the heart of the program is and this is what I would recommend suggest to go back and have a look because this is the main part of it all right thank you very much have good day bye e e e e