User input

0:00- [Lecturer] 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.

0:15The 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.

0:29But 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 wanna 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 every day works, we just know how to use it.

0:51So 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.

1:06We wanna 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.

1:19I'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 wanna display weather for 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.

1:42What if I also want a section on the page to display city name 10 day 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.

1:57Instead. Sounds like we wanna 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 wanna do with the output of an input function, because we wanna save that information that the user gave us.

2:10Then I can just access that variable anywhere. I wanna use the user's input. You may be thinking, "Hold up. You are 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 backend of an application.

2:27Most digital technology has a frontend and a backend. The backend is what the application does. It's the main logic and the data processing. The frontend is what the application looks and feels like. It's the visual or tactile elements that the user interacts with.

2:42The frontend and the backend then communicate. The frontend tells the backend what actions the user took, the backend processes that information, and then tells the frontend what data to display. Then the frontend takes that data and decides how to display it to the user.

2:55Both 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 gonna 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 gonna use my application either.

3:15Some programmers work on both back backend and frontend, but many programming teams are divided into backend developers and frontend developers because they're both such critical but different skill sets. Python is primarily a backend programming language. So when you use the input function, imagine there's a frontend that goes with it.

3:31If you wanna handle touch gestures on a phone, maybe your input prompt asks the user if they wanna 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.

3:44The backend's just returning the plain data, but the frontend 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 are easy to use, and it's thanks to backend developers that they do complex and interesting things.

4:05Let'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.