class ShareholderValue:
    """
    #### A class to represent shareholder value, which is the value created by a company that maximizes shareholder interests.

    Attributes:
    -----------
    earnings: float
        The earnings generated by the company.
    dividends: float
        The dividends paid to shareholders.
    stock_price: float
        The current market price of the company's stock.

    Methods:
    --------
    calculate_earnings_per_share():
        Calculates the earnings per share.
    calculate_dividend_yield():
        Calculates the dividend yield.
    calculate_price_earnings_ratio():
        Calculates the price-earnings ratio.
    """
    def __init__(self, independent, earnings, dividends, stock_price):
        self.earnings = earnings
        self.dividends = dividends
        self.stock_price = stock_price
        self._independent = independent
        self._independent.attach(self)
    def update(self):
        # 观察者收到通知后需要执行的操作
        print("Received notification from subject.")
    def unsubscribe(self):
        self._independent.detach(self)
    def calculate_earnings_per_share(self):
        """
        Calculates the earnings per share.
        """
        return self.earnings / self.calculate_number_of_shares()

    def calculate_dividend_yield(self):
        """
        Calculates the dividend yield.
        """
        return self.dividends / self.stock_price

    def calculate_price_earnings_ratio(self):
        """
        Calculates the price-earnings ratio.
        """
        return self.stock_price / self.calculate_earnings_per_share()

    def calculate_number_of_shares(self):
        """
        Calculates the number of shares.
        """
        # Calculate the number of shares outstanding based on company information.
        pass
