Functions - Exploration Tools

Welcome, @name! A good explorer doesn't perform every task from scratch. They have ready-made tools: one swing of the machete, one gesture to pitch the tent. In programming, such a reusable tool is called a function. A function is a named block of code that we can run whenever we want.

Defining a Function - the def Keyword

We create a function with the keyword `def` (from "define"). We give the function a name, parentheses and a colon, and below - an indented block of code.

1def greet_explorer():
2    print("🌴 Welcome to the Safari!")
3    print("Darwin wishes you a great expedition.")
4
5# Calling the function - we run it by its name
6greet_explorer()

Merely defining a function does not run it - it's like writing the instruction manual for a tool. To use the tool, we must call it by writing its name with parentheses: `greet_explorer()`. We can call it many times!

Parameters - Passing Data into a Function

A tool becomes more powerful when we can pass something to it. Parameters are data that a function accepts in parentheses.

1def greet_explorer(name):
2    print(f"🌴 Welcome, {name}, to the Safari!")
3
4greet_explorer("Darwin")   # 🌴 Welcome, Darwin, to the Safari!
5greet_explorer("Anna")     # 🌴 Welcome, Anna, to the Safari!

A function can accept multiple parameters:

1def describe_animal(species, weight):
2    print(f"{species} weighs {weight} kg.")
3
4describe_animal("Elephant", 5000)
5describe_animal("Lion", 190)

Returning a Value - the return Keyword

So far our functions only displayed text. But often we want a function to compute something and give us the result. That's what the `return` keyword is for.

1def calculate_speed(distance, time):
2    speed = distance / time
3    return speed
4
5# We can save the result to a variable
6result = calculate_speed(30, 4)
7print(f"Speed: {result} km/h")   # Speed: 7.5 km/h
8
9# Or use it right away
10print(f"Speed: {calculate_speed(60, 3)} km/h")

The difference is important: `print()` only shows text on the screen, while `return` gives back a value that we can use further in calculations. After `return` runs, the function ends immediately.

Functions with Conditions - Combining Knowledge

Functions can contain everything you've learned - conditions, loops, operators:

1def is_dangerous(weight):
2    if weight > 1000:
3        return True
4    else:
5        return False
6
7print(is_dangerous(5000))  # True (elephant)
8print(is_dangerous(190))   # False (lion)

Practice

Write a function that calculates how many days it takes to cover a given distance. Complete the code in the editor:

Summary

In this lesson you created your own explorer's tools:

• ✅ `def` - defines a function (a named block of code)
• ✅ Calling a function with `name()`
• ✅ Parameters - data passed into a function in parentheses
• ✅ `return` - returns a result that can be used further
• ✅ The difference between `print()` (displays) and `return` (gives back a value)

Congratulations! You now know the fundamentals of Python: variables, types, operators, conditions, loops, and functions. Time to combine this knowledge in a great expedition project! 🎉🌴