Having the deque with the advantages of Queue in a thread

user_1661267 0
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I need a structure where I will be able to pop() and append() to the right side (just like deque), while having the structure blocking and waiting if it is empty (just like Queue). I could directly use a Queue, but I need also the nice feature of deque where items are removed without blocking if the structure is full.

from collections import deque
d = deque(maxlen=2)
d.append(1)
d.append(2)
d.append(3) # d should be [2,3] (it is the case)
d.pop()
d.pop()
d.pop() # should wait (not the case)

Is it better to subclass deque (making it wait) or Queue (adding a popLeft function)?

deque queue python-3.x multithreading python
2 Answers

Not sure which is better, but here's an idea for adding wait on pop with threading.Event

from collections import deque
from threading import Event

class MyDeque(deque):
    def __init__(self, max_length):
        super().__init__(maxlen=max_length)
        self.not_empty = Event()
        self.not_empty.set()

    def append(self, elem):
        super().append(elem)
        self.not_empty.set()

    def pop(self):
        self.not_empty.wait()  # Wait until not empty, or next append call
        if not (len(q) - 1):
            self.not_empty.clear()
        return super().pop()

q = MyDeque(2)
q.append(1)
q.append(2)
q.append(3)
q.pop()
q.pop()
q.pop()  # Waits
user_45256000

What about creating your own queue mixing the best of both?

import queue as Queue
from collections import deque

class QueuePro:
  def __init__(self, maxlenDeque): 
    self.deque = deque(maxlen=maxlenDeque)
    self.queue = Queue.Queue()

  def append(self, elem):
    self.deque.append(elem)
    self.queue.put(elem)

  def pop(self):
    if(not self.deque):
      self.queue.get()
    else:
      self.deque.pop()
      self.queue.get()


q2 = QueuePro(2)
q2.append(1)
q2.append(2)

q2.pop()
q2.pop()
q2.pop()
#waiting
user_71280340
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