Walkthrough: Distance (Incremental Build)

例题: 距离 (增量构建)

≈ 10 min · python-decomposition python-functions · Open in WolfCode

Build distance() in four steps. Each step runs. Each step verifies one new thing. The textbook's most-quoted example of incremental development.

Python · runnable

import math

def area(radius):
    return math.pi * radius ** 2

def distance(x1, y1, x2, y2):
    dx = x2 - x1
    dy = y2 - y1
    return math.sqrt(dx ** 2 + dy ** 2)

def circle_area(xc, yc, xp, yp):
    radius = distance(xc, yc, xp, yp)
    return area(radius)

print("distance:", distance(1, 2, 4, 6))     # 5.0  (3-4-5 triangle)
print("area(5):", area(5))                   # ~78.54
print("circle_area:", circle_area(0, 0, 3, 4)) # area of radius 5 circle

Loading Python runtime (~5 MB, one-time)…

The four-step build

Skeleton: return 0.0 — verify it runs
Compute dx, dy: print them — verify diff calculation
Sum of squares: print dsquared — verify it equals 25
sqrt + remove scaffolding: final form