对复数1+2i 、3+4i、 6-7i 等对象进行抽象，声明复数类，并分析其属性和行为。

复数类（ComplexNumber）是对数学上复数的一种抽象，它通常包括实部（real part）和虚部（imaginary part）这两个基本属性。我们可以定义如下：

class ComplexNumber:
    def __init__(self, real=0, imag=0):
        self.real = real
        self.imag = imag

    # 属性访问方法
    @property
    def real(self):
        return self._real
    @real.setter
    def real(self, value):
        if not isinstance(value, (int, float)):
            raise ValueError("实部必须是数字")
        self._real = value

    @property
    def imag(self):
        return self._imag
    @imag.setter
    def imag(self, value):
        if not isinstance(value, (int, float)):
            raise ValueError("虚部必须是数字")
        self._imag = value

    # 行为方法：加法、减法、乘法、除法
    def add(self, other):
        real_sum = self.real + other.real
        imag_sum = self.imag + other.imag
        return ComplexNumber(real_sum, imag_sum)

    def subtract(self, other):
        real_diff = self.real - other.real
        imag_diff = self.imag - other.imag
        return ComplexNumber(real_diff, imag_diff)

    def multiply(self, other):
        real_prod = self.real * other.real - self.imag * other.imag
        imag_prod = self.real * other.imag + self.imag * other.real
        return ComplexNumber(real_prod, imag_prod)

    def divide(self, other):
        if other.real == 0 and other.imag == 0:
            raise ZeroDivisionError("除数不能为零")
        denominator = other.real ** 2 + other.imag ** 2
        real_quotient = (self.real * other.real + self.imag * other.imag) / denominator
        imag_quotient = (self.imag * other.real - self.real * other.imag) / denominator
        return ComplexNumber(real_quotient, imag_quotient)

    # 重写字符串方法，以便于输出
    def __str__(self):
        return f"{self.real} + {self.imag}i"

这个类包含了复数的基本属性（实部和虚部），以及常见的复数运算方法如加、减、乘、除。同时，为了方便用户查看复数，还实现了`__str__`方法，使得可以直接打印出复数的形式。