Functions

By the end of this step you can package steps into a named, reusable function, and you'll have written the heart of your description checker.

A function is a named recipe

You've been using functions already: print(), len(), round(), console.log(). Someone wrote them once; you use them by name. Now you'll write your own.

Three parts:

• The name (add_tax): what you call it by.
• Parameters (price): the inputs. Each time you call it, you fill them in: add_tax(100) runs the recipe with price set to 100.
• return: the result it hands back. Without a return, you get nothing back.

Why bother? Because you write the steps once, give them a clear name, and use them anywhere. When something's wrong, you fix it in one place.

Try it

# A function is a named recipe. "def" defines it; "return" hands back the result. def add_tax(price): return round(price * 1.08, 2) # "Calling" the function runs the recipe with the value you give it. print(add_tax(100)) print(add_tax(14.50)) # This one is the heart of the description checker you'll build. def word_count(text): words = text.split() # split() cuts text into words at the spaces return len(words) print(word_count("Light enough for thru-hikes")) print(word_count("")) # an empty description: 0 words, no crash # Types are a note about what goes in and what comes out. # Python doesn't enforce them, but your editor and your AI read them. def reading_minutes(words: int) -> float: return words / 200 # people read about 200 words a minute print(reading_minutes(word_count("Tested by our team on real trips"))) # Your turn: write a function is_too_short(text) that returns True # when a description has fewer than 20 words.

Output

Press Run (or Ctrl+Enter) to see the output here.

// A function is a named recipe. "function" defines it; "return" hands back the result. function addTax(price) { return Math.round(price * 1.08 * 100) / 100; } // "Calling" the function runs the recipe with the value you give it. console.log(addTax(100)); console.log(addTax(14.5)); // This one is the heart of the description checker you'll build. function wordCount(text) { const trimmed = text.trim(); // remove spaces at both ends if (trimmed === "") return 0; // an empty description: 0 words, no crash return trimmed.split(/\s+/).length; // /\s+/ means "one or more spaces" } console.log(wordCount("Light enough for thru-hikes")); console.log(wordCount("")); // In TypeScript you'd add types: function readingMinutes(words: number): number // Plain JavaScript (what runs here) leaves them out. function readingMinutes(words) { return words / 200; // people read about 200 words a minute } console.log(readingMinutes(wordCount("Tested by our team on real trips"))); // Your turn: write a function isTooShort(text) that returns true // when a description has fewer than 20 words.

Output

Press Run (or Ctrl+Enter) to see the output here.

word_count is the core of the tool you're about to build. Notice it copes with an empty description (""): it returns 0 instead of crashing. JavaScript needs an extra line for that (if (trimmed === "") return 0;): splitting empty text in JavaScript gives you a list with one empty item in it, which would count as 1 word. Little differences like this are why you test the odd cases, not just the normal ones.

Types: a note on what goes in and out

def reading_minutes(words: int) -> float: says: this takes a whole number and gives back a decimal number. Those notes are types. In Python they're optional and nothing checks them while the program runs, but your editor and your AI read them and warn you about mistakes. TypeScript is JavaScript with types added (function readingMinutes(words: number): number). You'll see types throughout the course; they're the contract that says what a piece of code expects.

Your turn

Write a function is_too_short(text) (JavaScript: isTooShort(text)) that returns true when a description has fewer than 20 words. Test it on a short sentence and a long one.

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