DSA 19: Queues - Print [Part 2]

1. Build a PrintManager class

1.1 The Task

• Build a simple Python interface for a printer that can accept printing jobs.
• Ensure print each document in the order in which it was received.

2. Psuedo-Code Solution

2.1 Add Queue class:

• enqueue(value): add value to queue
• dequeue(): remove first item from queue
• read(): peek at first from queue

2.2 Add Printer class:

• add_job_to_queue(job): add job to queue
• print(job): print job
• run():
  • dequeue() each job then
  • print(job) from front to back

3. Python-Code Solution

3.1 Queue class

From queue class implementation post.

class Queue:
    def __init__(self):
        self.data = []
        
    def enqueue(self,value):
        self.data.append(value)
        
    def dequeue(self):
        if len(self.data)>0:
            return self.data.pop(0)
        else:
            return None

    def read(self):
        if len(self.data)>0:
            return self.data[0]
        else:
            return None
    
    def __repr__(self):
        return f"{self.data!r}"

    # def __str__(self):
    #     print(f"{self.data!r}")
    

3.2 Queue: Testing

tp_q = Queue()
tp_q.enqueue(1)
print(tp_q)

tp_q.enqueue(2)
print(tp_q)

tp_q.enqueue(3)
print(tp_q)

tp_q.dequeue()
print(tp_q)

tp_q.enqueue(4)
print(tp_q)

tp_q.enqueue(5)
print(tp_q)
tp_q.enqueue(6)
print(tp_q)
tp_q.dequeue()
print(tp_q)
tp_q.dequeue()
print(tp_q)
tp_q.dequeue()
print(tp_q)
tp_q.dequeue()
print(tp_q)
tp_q.dequeue()
print(tp_q)
tp_q.dequeue()

[1]
[1, 2]
[1, 2, 3]
[2, 3]
[2, 3, 4]
[2, 3, 4, 5]
[2, 3, 4, 5, 6]
[3, 4, 5, 6]
[4, 5, 6]
[5, 6]
[6]
[]

3.3 PrintManager class

class PrintManager():
    def __init__(self):
        self.queue = Queue()
    
    def add_job(self, job):
        self.queue.enqueue(job)
        print(f"{job!r} added: {self.queue}")
    
    def run(self):
        while self.queue.read():
            current_job = self.queue.dequeue()
            self.print_job(current_job)
    def print_job(self,job):
        print(job)
    

3.4 PrintManager class: Testing

printer = PrintManager()
printer.add_job("doc1.md")
printer.add_job("doc2.docx")
printer.add_job("doc3.pdf")
printer.run()

'doc1.md' added: ['doc1.md']
'doc2.docx' added: ['doc1.md', 'doc2.docx']
'doc3.pdf' added: ['doc1.md', 'doc2.docx', 'doc3.pdf']
doc1.md
doc2.docx
doc3.pdf