#!/usr/bin/env python
from __future__ import print_function


class Element(object):
    ''' Create data element with default value and next pointer. '''
    def __init__(self, value, ahead=None, behind=None, priority=0):
        ''' Value and next pointer default to none. '''
        self.val = value
        self.ahead = ahead
        self.behind = behind
        self.prio = priority


class Priorityq(object):
    ''' Create an empty queue. '''
    def __init__(self):
        self.front = None
        self.back = None

    def insert(self, value):
        ''' Add data element to the back of queue. '''
        new_element = Element(value, self.back)

        if not self.front:
            self.front = self.back = new_element
        elif new_element.prio <= self.back.prio:
            new_element.ahead, self.back = self.back, new_element
        else:
            self.__prioritize(new_element)

    def __prioritize(self, new_element):

        current = self.back.ahead

        while True:
            if new_element.prio <= current.prio:
                new_element.behind = current
                new_element.ahead.behind.ahead = new_element
                new_element.behind = new_element.ahead.behind
                new_element.ahead.behind = new_element
                return
            else:
                try:
                    current = current.ahead
                except AttributeError:
                    new_element.behind, self.front = self.front, new_element
                    return

    def dequeue(self):
        ''' Remove front element from front of queue. Reassign front data
            element and return value of dequeued element. '''
        try:
            val = self.front.val
        except AttributeError:
            ''' Mimic error message from list '''
            raise IndexError("dequeue from empty Stack")
        self.front.behind.ahead, self.front = None, self.front.behind
        return val

    def size(self):
        ''' Return size of queue (number of elements). '''
        count = 0
        current = self.back
        while current:
            count += 1
            current = current.ahead
        return count

@@ -1528,23 +1528,19 @@
     def 
-dequeue
+pop
 (self):%0A
@@ -1551,634 +1551,122 @@
     
-''' Remove front element from front of queue. Reassign front data%0A            element and return value of dequeued element. '''%0A        try:%0A            val = self.front.val%0A        except AttributeError:%0A            ''' Mimic error message from list '''%0A            raise IndexError(%22dequeue from empty Stack%22)%0A        self.front.behind.ahead, self.front = None, self.front.behind%0A        return val%0A%0A    def size(self):%0A        ''' Return size of queue (number of elements). '''%0A        count = 0%0A        current = self.back%0A        while current:%0A            count += 1%0A            current = current.ahead%0A        return count
+pop_value = self.front%0A        self.front.behind.ahead, self.front = None, self.front.behind%0A        return pop_value
 %0A

Add pop() function