abstracted structure edited in the book

src/abstract_structures/queues/queue.py

@@ -0,0 +1,63 @@
+#!/usr/bin/env python
+
+__author__ = "bt3"
+
+
+class Queue(object):
+
+    def __init__(self):
+        self.in_stack = []
+        self.out_stack = []
+
+    def _transfer(self):
+        while self.in_stack:
+            self.out_stack.append(self.in_stack.pop())
+
+    def enqueue(self, item):
+        return self.in_stack.append(item)
+
+    def dequeue(self):
+        if not self.out_stack:
+            self._transfer()
+        if self.out_stack:
+            return self.out_stack.pop()
+        else:
+            return "Queue empty!"
+
+    def size(self):
+        return len(self.in_stack) + len(self.out_stack)
+
+    def peek(self):
+        if not self.out_stack:
+            self._transfer()
+        if self.out_stack:
+            return self.out_stack[-1]
+        else:
+            return "Queue empty!"
+
+    def __repr__(self):
+        if not self.out_stack:
+            self._transfer()
+        if self.out_stack:
+            return '{}'.format(self.out_stack)
+        else:
+            return "Queue empty!"
+
+    def isEmpty(self):
+        return not (bool(self.in_stack) or bool(self.out_stack))
+
+
+if __name__ == '__main__':
+    queue = Queue()
+    print("Is the queue empty? ", queue.isEmpty())
+    print("Adding 0 to 10 in the queue...")
+    for i in range(10):
+        queue.enqueue(i)
+    print("Queue size: ", queue.size())
+    print("Queue peek : ", queue.peek())
+    print("Dequeue...", queue.dequeue())
+    print("Queue peek: ", queue.peek())
+    print("Is the queue empty? ", queue.isEmpty())
+
+    print("Printing the queue...")
+    print(queue)