"""Solution 6.3.1 — Relying on a shared method

Chapter 6: Objects — Everyday Programming

Bug type: Runtime

shape.area refers to the method without calling it, so adding it to a
number raises a TypeError. Calling shape.area() invokes each shape's
method and totals the areas to 25.0.

Exercise: ex_6_3_1.py
"""

class Square:
    def __init__(self, side):
        self.side = side

    def area(self):
        return self.side * self.side

class Triangle:
    def __init__(self, base, height):
        self.base = base
        self.height = height

    def area(self):
        return self.base * self.height / 2

def total_area(shapes):
    total = 0
    for shape in shapes:
        total = total + shape.area()
    return total

print(total_area([Square(4), Triangle(6, 3)]))   # 25.0