设计三角形类，继承图形抽象类，计算三角形面积和周长

from abc import ABC, abstractmethod
import math

class Shape(ABC):
    
    @abstractmethod
    def area(self):
        pass
    
    @abstractmethod
    def perimeter(self):
        pass

class Triangle(Shape):
    
    def __init__(self, a, b, c):
        self.a = a
        self.b = b
        self.c = c
    
    def area(self):
        s = (self.a + self.b + self.c) / 2
        return math.sqrt(s * (s - self.a) * (s - self.b) * (s - self.c))
    
    def perimeter(self):
        return self.a + self.b + self.c

使用示例：

t = Triangle(3, 4, 5)
print(t.area())
print(t.perimeter())

输出：

6.0
12