User input | Intro to CS - Python | Khan Academy

what are some of the ways you interact with digital technology every day you might press a button enter something into a text box or swipe up or down you might even move a joystick on a controller tap a credit card or turn a knob on a car these are all ways that a program can ask for input from a user the program waits for the user's response and then reacts to it in Python we can ask the user for input with the input function when I run this program I see a blinking cursor appear in

the console if I type something in here and hit enter the program terminates but what happened to that value that I entered it's there the computer received it but just like any value we can't see it unless we tell the computer to print it when we use the input function we want to think about our user interface the person using our program may be someone else who doesn't know anything about our code just how we don't know how the programming behind most of the technology we use everyday works we just know how to use it

so we need to make sure we're giving the user enough information so they know what to enter when they see the prompt luckily for us the input function takes a single input value whatever string we put inside these parentheses will show up in the console on the same line right before that blinking cursor we want to make this prompt message descriptive so the user knows what we're asking for maybe they need to choose between a few values or enter a date here let's imagine we're building a weather app and we want the user to enter

a city so we can load the weather for it I'll add a descriptive prompt here to make sure the user knows we're looking for a city name by convention we usually add a single space character at the end of any prompt message so we get a space in the console between the message and the cursor at the top of the app I want to display weather four city name so I'm just going to concatenate that to the front of the input call because we know the input function returns out whatever string the user entered at

the prompt what if I also want a section on the page to display city name 10day forecast if I add another input function call now two prompts show up in the console so the user has to enter the city name twice and there's no guarantee that they enter the same city name both times instead sounds like we want to store that first city name that the user entered so we can use it later this calls for a variable in most cases this is the first thing you want to do with the output of an input

function because we want to save that information that the user gave us then I can just access that variable anywhere I want to use the user's input you may be thinking hold up you were talking about tapping a credit card or swiping on my phone not typing something into this janky prompt in the console it's not because we're building fake programs it's because we're working on the back end of an application most digital technology has a front end and a back end the back end is what the application does it's the main logic in the

data processing the front end is what the application looks and feels like it's the visual or tactile elements that the user interacts with the front end and the back end then communicate the front end tells the back end what actions the user took the backend processes that information and then tells the front end what data to display then the front end takes that data and decides how to display it to the user both parts are equally important if I have a game where the controls are super confusing and show up in unexpected places on the

screen then no one's going to play my game even if it's the coolest game ever on the other hand if I have a beautifully designed website with an easy to navigate layout but the search results are garbage and everything's slow to load no one's going to use my application either some programmers work on both backend and front-end but many programming teams are divided into backend developers and front-end developers because they're both such critical but different skill sets python is primarily a back-end programming language so when you use the input function imagine there's a front end

that goes with it if you want to handle touch gestures on a phone maybe your input promp asks the user if they want to swipe right left up or down or if it's a text box then maybe the prompt is just the label for it like search or subject you can imagine your print output the same way the back end's just returning the plain data but the front end would lay it out nicely on the screen so if you ever start feeling like hey this console input output thing feels kind of blah remember that most

programs don't look fancy either it's thanks to front end developers that applications look cool and easy to use and it's thanks to back and developers that they do complex and interesting things let's focus on mastering one thing at a time though for us that means making our programs do cool things and we'll worry about how they look later