class_docstr: A `.Queue` that retrieves entries in priority order, lowest first.
  
  Entries are typically tuples like ``(priority number, data)``.
  
  .. testcode::
  
      from tornado.queues import PriorityQueue
  
      q = PriorityQueue()
      q.put((1, 'medium-priority item'))
      q.put((0, 'high-priority item'))
      q.put((10, 'low-priority item'))
  
      print(q.get_nowait())
      print(q.get_nowait())
      print(q.get_nowait())
  
  .. testoutput::
  
      (0, 'high-priority item')
      (1, 'medium-priority item')
      (10, 'low-priority item')
class_docstr_tok: ["A","`",".Queue","`","that","retrieves","entries","in","priority","order",",","lowest","first",".","Entries","are","typically","tuples","like","``","(","priority","number",",","data",")","``",".","..","testcode",":",":","from","tornado.queues","import","PriorityQueue","q","=","PriorityQueue","(",")","q.put","(","(","1",",","'medium-priority","item","'",")",")","q.put","(","(","0",",","'high-priority","item","'",")",")","q.put","(","(","10",",","'low-priority","item","'",")",")","print","(","q.get_nowait","(",")",")","print","(","q.get_nowait","(",")",")","print","(","q.get_nowait","(",")",")","..","testoutput",":",":","(","0",",","'high-priority","item","'",")","(","1",",","'medium-priority","item","'",")","(","10",",","'low-priority","item","'",")"]
code: def _init(self):
      self._queue = []
  
imports: from __future__ import absolute_import, division, print_function
  import collections
  import heapq
  from tornado import gen, ioloop
  from tornado.concurrent import Future
  from tornado.locks import Event
label_desc: Use image node_id 1 for calling the PriorityQueue obj's underlying member method code with example usage: obj._init() without return types