Python实现时钟页面替换算法的代码

以下是Python实现时钟页面替换算法的代码：

class Page(object):
    def __init__(self, page_id, reference_bit):
        self.page_id = page_id
        self.reference_bit = reference_bit


class ClockPageReplacement(object):
    def __init__(self, page_frames):
        self.page_frames = page_frames
        self.hand = 0
        self.pages = [None] * page_frames

    def page_fault(self, page_id):
        while True:
            page = self.pages[self.hand]
            if page is None:
                self.pages[self.hand] = Page(page_id, True)
                self.hand = (self.hand + 1) % self.page_frames
                return True
            elif page.reference_bit:
                page.reference_bit = False
            else:
                page.page_id = page_id
                page.reference_bit = True
                self.hand = (self.hand + 1) % self.page_frames
                return True

    def access_page(self, page_id):
        for page in self.pages:
            if page and page.page_id == page_id:
                page.reference_bit = True
                return
        self.page_fault(page_id)

    def __str__(self):
        return ', '.join(str(page.page_id) if page else '-' for page in self.pages)

使用时钟页面替换算法，可以创建ClockPageReplacement对象，然后调用access_page方法来访问页面。如果页面不在页帧中，则会发生页面故障并替换页面。最后，调用__str__方法可以打印当前页帧中的页面情况。例如：

clock = ClockPageReplacement(3)
clock.access_page(1)
clock.access_page(2)
clock.access_page(3)
print(clock) # 1, 2, 3
clock.access_page(4)
print(clock) # 4, 2, 3
clock.access_page(3)
print(clock) # 4, 2, 3
clock.access_page(1)
print(clock) # 4, 1, 3