python - 如何在 Python 中创建模拟打印机？

Question

我正在尝试使用链接队列来模拟打印机来管理打印作业。一个打印作业会按照提交的先后顺序进行处理，有2台打印机。每个打印作业都有多个页面，并且会在用户选择的特定循环次数内占用打印机。

因此，例如，如果有 3 个作业，作业 1(5 页)、作业 2(7 页)和作业 3(13 页)，在 6 个循环(打印页)之后，一台打印机将打印作业 2还剩 1 页，另一个将有作业 3，还剩 12 页。

我能够处理队列中的 2 个作业，但我不知道如何处理第三个作业，因为我希望仅当打印机可用时才处理第三个作业。

Answer 1

这是您所能找到的最清晰的解决方案 - 三个类(PrintJob、JobQueue 和 Printer)和一个main() 函数进行模拟:

class PrintJob:
    def __init__(self, name, pages):
        self.name = name
        self.pages = pages
        self.remaining = pages

    def tick(self):
        if self.remaining:
            self.remaining -= 1
        print("Job {}: {} / {} pages remain".format(self.name, self.remaining, self.pages))

    def is_done(self):
        return self.remaining == 0

class JobQueue:
    def __init__(self):
        self.jobs = []

    def enqueue(self, job):
        self.jobs.append(job)

    def dequeue(self):
        return self.jobs.pop(0)

    def is_empty(self):
        return not self.jobs

class Printer:
    def __init__(self, name, job_queue):
        self.name = name
        self.job_queue = job_queue
        self.current_job = None

    def tick(self):
        # make sure we have a job to work on
        if self.current_job is None:
            if self.job_queue.is_empty():
                print("Printer {} is idle".format(self.name))
                return
            else:
                self.current_job = self.job_queue.dequeue()
                print("Printer {} got job {}".format(self.name, self.current_job.name))
        # print!
        print("Printer {} is printing...".format(self.name))
        self.current_job.tick()
        # see if job is finished
        if self.current_job.is_done():
            print("Printer {} finished job {}".format(self.name, self.current_job.name))
            self.current_job = None

    def is_idle(self):
        return self.current_job is None

def main():
    # create job queue and two printers
    jobs = JobQueue()
    p1 = Printer(1, jobs)
    p2 = Printer(2, jobs)

    # add jobs
    jobs.enqueue(PrintJob(1, 5))
    jobs.enqueue(PrintJob(2, 7))
    jobs.enqueue(PrintJob(3, 13))

    # cycle until queue is empty
    tick = 0
    while not (jobs.is_empty() and p1.is_idle() and p2.is_idle()):
        tick += 1
        print("\n=== Tick {} ===".format(tick))
        p1.tick()
        p2.tick()

    print("\nAll done! Time for a pint...")

if __name__ == "__main__":
    main()

最后的结果是这样的

=== Tick 1 ===
Printer 1 got job 1
Printer 1 is printing...
Job 1: 4 / 5 pages remain
Printer 2 got job 2
Printer 2 is printing...
Job 2: 6 / 7 pages remain

=== Tick 2 ===
Printer 1 is printing...
Job 1: 3 / 5 pages remain
Printer 2 is printing...
Job 2: 5 / 7 pages remain

=== Tick 3 ===
Printer 1 is printing...
Job 1: 2 / 5 pages remain
Printer 2 is printing...
Job 2: 4 / 7 pages remain

=== Tick 4 ===
Printer 1 is printing...
Job 1: 1 / 5 pages remain
Printer 2 is printing...
Job 2: 3 / 7 pages remain

=== Tick 5 ===
Printer 1 is printing...
Job 1: 0 / 5 pages remain
Printer 1 finished job 1
Printer 2 is printing...
Job 2: 2 / 7 pages remain

=== Tick 6 ===
Printer 1 got job 3
Printer 1 is printing...
Job 3: 12 / 13 pages remain
Printer 2 is printing...
Job 2: 1 / 7 pages remain

=== Tick 7 ===
Printer 1 is printing...
Job 3: 11 / 13 pages remain
Printer 2 is printing...
Job 2: 0 / 7 pages remain
Printer 2 finished job 2

=== Tick 8 ===
Printer 1 is printing...
Job 3: 10 / 13 pages remain
Printer 2 is idle

=== Tick 9 ===
Printer 1 is printing...
Job 3: 9 / 13 pages remain
Printer 2 is idle

=== Tick 10 ===
Printer 1 is printing...
Job 3: 8 / 13 pages remain
Printer 2 is idle

=== Tick 11 ===
Printer 1 is printing...
Job 3: 7 / 13 pages remain
Printer 2 is idle

=== Tick 12 ===
Printer 1 is printing...
Job 3: 6 / 13 pages remain
Printer 2 is idle

=== Tick 13 ===
Printer 1 is printing...
Job 3: 5 / 13 pages remain
Printer 2 is idle

=== Tick 14 ===
Printer 1 is printing...
Job 3: 4 / 13 pages remain
Printer 2 is idle

=== Tick 15 ===
Printer 1 is printing...
Job 3: 3 / 13 pages remain
Printer 2 is idle

=== Tick 16 ===
Printer 1 is printing...
Job 3: 2 / 13 pages remain
Printer 2 is idle

=== Tick 17 ===
Printer 1 is printing...
Job 3: 1 / 13 pages remain
Printer 2 is idle

=== Tick 18 ===
Printer 1 is printing...
Job 3: 0 / 13 pages remain
Printer 1 finished job 3
Printer 2 is idle

All done! Time for a pint...