定义一个类，根据输入点数不同，分别计算三角形和正方形面积和周长。写这个的代码

好的，这是一个可以执行上述操作的 Python 类的代码示例：

class Shape:
    def __init__(self, n):
        self.n = n

    def calculate_area(self):
        if self.n == 3:
            # calculate area of triangle
            side_a = float(input("Enter the length of side a: "))
            side_b = float(input("Enter the length of side b: "))
            side_c = float(input("Enter the length of side c: "))
            s = (side_a + side_b + side_c) / 2
            area = (s * (s - side_a) * (s - side_b) * (s - side_c)) ** 0.5
            print(f"The area of the triangle is {area:.2f} square units.")
        elif self.n == 4:
            # calculate area of square
            side = float(input("Enter the length of a side: "))
            area = side ** 2
            print(f"The area of the square is {area:.2f} square units.")
        else:
            print("Invalid input.")

    def calculate_perimeter(self):
        if self.n == 3:
            # calculate perimeter of triangle
            side_a = float(input("Enter the length of side a: "))
            side_b = float(input("Enter the length of side b: "))
            side_c = float(input("Enter the length of side c: "))
            perimeter = side_a + side_b + side_c
            print(f"The perimeter of the triangle is {perimeter:.2f} units.")
        elif self.n == 4:
            # calculate perimeter of square
            side = float(input("Enter the length of a side: "))
            perimeter = 4 * side
            print(f"The perimeter of the square is {perimeter:.2f} units.")
        else:
            print("Invalid input.")

要使用这个类，只需要创建一个对象并调用相应的方法即可。例如：

my_shape = Shape(3)
my_shape.calculate_area()     # prompts user to input side lengths and calculates area of triangle
my_shape.calculate_perimeter()     # prompts user to input side lengths and calculates perimeter of triangle

如果点数输入错误，类会输出 `"Invalid input."` 。

请问还有什么问题需要我解答吗？