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Hello, friends, in this video, we shall try and write our first flash application or less Hello World.

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Hello, World is invariably the first program that you write whenever you learn a new technology.

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So here also we shall see how to write or how to generate Hello World from our application.

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First and foremost, you are to import the last module.

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More specifically, you have to import the flask, a glass from the flask module that is mandatory,

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then you have to instantiate or you go to create an object of the flask.

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Plus that object of the flask class becomes our application object.

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It is an object for our WGI application.

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So these two steps are in the right in the beginning of your of our coal importing the flask Maryland

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class class and creating the object of.

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Now, you know that whenever an object of a class is instantiated, the constructor starts to work,

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so the class constructor also will be executed.

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And it takes one argument inside the underscore name, and it is the name of the current module that

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is the argument for the object.

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Then you are to use a function, root, root function of the last class is to be used to define the

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new order and map a particular view, function with the, you know, use the rule.

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So this root function is called as a decorator, which does the application which you are allowed to

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be, which when a particular order is given, which is the function that is to be executed, that association

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is defined by the root function.

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So this is the way in which this rule function is used.

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Eppy, the app, the name of the object of our Flast plus eppy, that route two arguments will be the

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rule.

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Rule is the other options are of course they are optional.

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They may not be appearing every time Ruri parameter represents the you are which is bound to a particular

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function.

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So FPP not route whichever you are you want if at all, for the root function.

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You, you want to pass certain parameters.

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Those parameters can be given as the options.

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So this is the syntax of the rule decorator's.

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After the rules are defined by the rules decorator, you have to run the application by calling the

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meter.

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So Eppy not run.

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It takes four parameters are for arguments, one is the host.

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The host on which your application will listen for the requests, the default is the local news.

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You can also identify the local lost by 127 one zero point zero one is the IP address of the local host.

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If you want this development server to be available from the external IP, then you can set it to zero

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zero zero.

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Board, no, we know that the Web server is bound to hostname and port names the default, what number

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is five thousand?

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You can change if you want.

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Debug option can be, you know, enabled or disabled depending on the requirement.

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What is the purpose of the debug option?

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I will tell you just afterwards and any other options that may be required to be passed to this Web

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server.

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So these are the four option four parameters that are required to this.

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So this is a sample code of a simple hello flask application, as I said in the beginning, to import

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the flask from the last module from flask, import, flask, OK, then create or declare an object applicable

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to flask takes one argument the name of the module in which it is named.

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Now this is the definition of the rule.

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I'm giving a slash at Eppy dot route.

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Not to this.

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You are in this function is mapped.

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What is the name of the function?

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I know what this is called a review function.

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When this you are it is given this function will be executed.

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And in turn what, what it will do, it will return this string.

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Hello.

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That will be rendered on your browser.

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This is of course the syntax or mechanism that you generally use to execute the module as the mean.

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Now when this Python script is executed, when you run this script by saying Python, hello, why?

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If this this script is named as PUA by Tom Hello Rajput, what happens?

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The server will start the WGI server development server will start and it will tell you in the python

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shell that it is running on STP.

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This localhost, the server starts running so the program is run.

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These are already started, started running.

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All you have to do now is to go to the browser.

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In that bar you either you can give one twenty zero zero one current five thousand or you can you localhost

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firefighters one and see what happens as soon as this.

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You are really given this one, this HelloWallet function will be executed.

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It will return.

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Hello.

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Hello.

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World as a string and it will be rendered on your browser.

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So that is the simplest way of generating or displaying world on your browsers page through the application.

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Now, you found that there is a debug option to the running method.

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Usually what happens when you are in a process of developing an application, you frequently want to

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make certain changes into it.

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So every time and are certain modifications or changes done, you may have to stop the server or when

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the program listing make the corrections and again run it.

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So this is a slightly tedious process.

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So you can avoid that by setting the deeper option to do so.

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If you step debugging, you want to prove no need to stop the program, stop the server chip, make

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the changes, save it and run it every time.

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You don't have to do this in each other, even if the server is running.

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You can go back to your code, make certain changes, save it.

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The server will automatically sense that a certain change has been done and it will automatically reload

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the contents of your backend program.

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So that is the benefit of setting the table is equal to as can be used when is set up or debug ep the

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name of the object that you want to prove and then run.

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Or you can use this debugging you want to do inside the Blackwaters.

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So what ways you can do it?

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The benefit of it is that while developing you don't have to face the hassles of stopping and starting

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like this.

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Lastly, when you say that when you run the program.

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In the development environment, the development environment is available only on the local machine

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on which the environment has been set up.

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Because the development support has been enabled, so when their support has been enabled, the support

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is available only on the local machine.

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If you want to make this application available to the external IP address, then what you have to do,

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you are to set another parameter hostage equal if you say is equal to zero zero zero zero, and if your

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computer is having a, you know, connection with the outside world.

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If it is having a static IP sort of thing, then this application, the application that you have written,

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may be available or will be available to the externally external environment so that your server will

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become an externally visible server.

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So these activities now, I will practically demonstrate in front of you so that you will be able to

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find out how exactly to write a hello world application so far.

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We have successfully installed flask.

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In our virtual environment now, we shall write a simple hello world application using Flast, so first

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line is required to import the flask module into our application.

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Next is to create a flask object.

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Which takes the constructor of the flask plastic's one argument, which is the name of the current module

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and that is retrieved by that will underscore the name of the school.

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Then you are to use the rope.

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Method of the flask object.

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What Israel is doing is route is called the corridor, which tells the flask server, which is the.

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You know, function, which is associated with this, you are.

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So which means that this forward slash you want in front of the record, in the room means that this

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forward slash is attached to this function.

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So if I invoke the server and you.

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This forward slash in front of the name of the server.

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Then this function will be executed.

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So.

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When this.

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Script will be run, the AP did maybe not run, run function, then Metalious available to this flask

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object that will be executed and accordingly, whichever path that you mention in the you are in the

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associated function will be called.

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So what I am going to do is I run this application from the python, from the Python prompt will show

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me that the server is running and then we will open the browser to see the world message that is being

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printed.

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So this was.

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The script of the Hello World application.

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Now, Norwegian.

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Start the application, our virtual environment is in the flask in redirect.

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So first we have to activate it by seeing.

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Activity, which is in the scripts folder of the class in the Virtual Environment Directorate.

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So it will be activated.

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Then we are to run the script out by.

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So if I press enter, what will happen?

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The message will be they're telling me that the server is running on.

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One twenty seven point zero one zero zero one zero point one.

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That is the address of the localhost, the default for these five thousand, so on this, the server

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is running.

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So if I.

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Go to the browser, give this URL, I should be able to see the hello world message being printed.

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So let us open the browser and give the Yoran, as you know, being displayed there.

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Now we shall see how the debugged support can be enabled in the flask application.

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Actually, our application is right now running.

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At the U.N., you are so I will first stop it by control.

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And then.

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Inability work, supervising the work equal to two.

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And ran the application.

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You see, there are certain changes in the output that is being displayed.

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It says that the weather is active and it is the application is running on the same.

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You are.

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OK, so if you again go back to this localhost Quillen 5000, and it will again show you the whole.

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So the hello world is displayed now, what is the effect of this debuggers equal to?

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If the devil is not set equal to two.

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And if the application is running after the app while the application is running, if you make any changes

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to the Python script.

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Then for every change that you may have, you may want to make to this fight on application, you know,

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to stop this or make the changes, restart the server and then.

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Open the browser now that they're debug is through the work, support is enabled.

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What you can do while the server is running itself.

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You can do whatever changes you want.

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Those changes will be automatically refreshed without you having to stop and restart the server.

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That is the advantage of Diebel.

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Our application is already running in the world more than the work is set equal to do you know what

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I will do?

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I will make certain changes here.

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Something like this.

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And save this.

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As soon as I see you, you see that.

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That is saying detect change in the script, and it is reassuring it.

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So this is what happens when you.

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And they will debate more now if I go back to the browser and just refresh it, I should be able to

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see the Halo tutorial point instead of Hellewell.

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You do not have to stop this or make the changes and then again relaunch it.

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So it has already reloaded the script.

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And just refresh this.

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That is why the changes have been automatically incorporated.

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So this is how the debug effect, neocortical through, affects the behavior of the.

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Server.