Talking to Your Computer

By default, Python programs run from top to bottom without stopping. To make a program interactive, we use the input() function. Think of this function as a 'pause button.' When Python hits an `input()` line, it stops and waits for the user to type something and press the Enter key. The text the user types is then handed back to the program as a string. Even if the user types a number like $42$, Python treats it as text characters '4' and '2' unless we tell it otherwise. We usually store this information in a variable so we can use it later, like this: $user\_name = input("What is your name? ")$.

Once you have captured data in a variable, you need a way to show it back to the user. In the past, joining text and variables was messy. Now, we use f-strings (formatted strings). To create one, put the letter $f$ right before the opening quotation mark. This tells Python to look inside the string for curly braces $\{ \}$. Anything inside the braces is treated as code or a variable name. For example, if $score = 10$, then $f"Your score is \{score\}"$ becomes "Your score is 10". It is a clean, fast way to build sentences that change based on user data.

Interactive programs are most powerful when they use multiple pieces of data to create a unique experience. You can use the input() function multiple times in a row to gather a 'profile' of the user. Remember that the order matters: you must define a variable using `input()` before you try to use it in a `print()` statement. If you try to print a variable that hasn't been assigned yet, Python will throw a NameError. Good interactive design also includes a space at the end of your input prompt string so the user's typing doesn't touch your question text.