W WolfCode · CSC 141

Chapter · Functions

Walkthrough: Square & Cube

例题: 平方和立方

≈ 8 min · python-functions · Open in WolfCode

The minimum-viable function example — three fruitful functions that compose. def + return + a function calling another.

The three functions

Python · runnable

def square(n):
    return n * n

def cube(n):
    return square(n) * n         # composition: cube uses square

def sum_of_powers(n):
    return n + square(n) + cube(n)

print(square(5))             # 25
print(cube(3))               # 27
print(sum_of_powers(2))      # 14

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Anatomy of `def square(n):`

def — keyword that introduces a function definition
square — the function's name (same rules as variable names)
(n) — one parameter
: — separates header from body
return n * n — sends the result back to the caller

The fruitful-vs-void trap

A function that prints isn't the same as one that returns

def square_VOID(n):
    print(n * n)            # prints but doesn't return

x = square_VOID(5)          # screen shows 25
print("x is:", x)           # x is: None

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Composition in action — trace `sum_of_powers(2)`

sum_of_powers(2) evaluates 2 + square(2) + cube(2)
square(2) → returns 4
cube(2) → calls square(2) → returns 4, then * 2 → 8
sum: 2 + 4 + 8 → 14

Next

Try modifying the example, then move to Clamp — your first function with three parameters.