Priority queue in Python

Author: Deepali-Srivastava

stack-and-queue/priority-queue.py

@@ -0,0 +1,95 @@
+# Copyright (C) Deepali Srivastava - All Rights Reserved
+# This code is part of DSA course available on CourseGalaxy.com  
+
+class EmptyQueueError(Exception):
+    pass
+
+class Node:
+
+    def __init__(self,value,pr):
+        self.info = value 
+        self.priority = pr
+        self.link = None 
+        
+class PriorityQueue:
+
+    def __init__(self):
+        self.front = None
+
+    def enqueue(self, data, data_priority):
+
+        temp = Node(data, data_priority)
+        
+        #If queue is empty or element to be added has priority more than first element
+        if self.is_empty() or data_priority < self.front.priority:
+            temp.link = self.front
+            self.front = temp
+        else:
+            p = self.front
+            while p.link != None and p.link.priority <= data_priority:
+                p = p.link
+            temp.link = p.link
+            p.link = temp
+                 
+    def dequeue(self):
+        if self.is_empty():
+            raise EmptyQueueError("Queue is empty")
+        x = self.front.info
+        self.front = self.front.link
+        return x
+    
+    def is_empty(self):
+        return self.front == None
+            
+    def display(self):
+        if self.is_empty():
+            print("Queue is empty")
+            return
+
+        print("Queue is : ")
+        p = self.front 
+        while p is not None:
+            print(p.info , "     ", p.priority)
+            p = p.link 
+        print()
+    
+    def size(self):
+        n = 0
+        p = self.front 
+        while p is not None:
+            n+=1
+            p = p.link
+        return n
+    
+    
+    
+#########################################################################################
+
+if __name__ == "__main__":
+    qu = PriorityQueue()
+
+    while True:
+        print("1.Enqueue") 
+        print("2.Dequeue") 
+        print("3.Display all queue elements") 
+        print("4.Display size of the queue")  
+        print("5.Quit") 
+         
+        choice = int(input("Enter your choice : "))
+
+        if choice == 1:
+            x = int(input("Enter the element : "))
+            pr = int(input("Enter its priority : "))
+            qu.enqueue(x,pr) 
+        elif choice == 2:
+            x=qu.dequeue() 
+            print("Element is : " , x) 
+        elif choice == 3:
+            qu.display() 
+        elif choice == 4:
+            print("Size of queue " , qu.size()) 
+        elif choice == 5:
+          break;
+        else:
+          print("Wrong choice") 
+        print()