The ‘push’<\/strong> action, as shown in the diagram below, places an element on the top of the stack. see the image for a better understanding:<\/p>\n The ‘pop’<\/strong> action, as shown in the diagram below, takes off an element from the top of the stack. see the image for a better understanding:<\/p>\n In Python, we can make a stack using the built-in List, which has methods that mimic both stack and queue actions. Alternatively, the deque library in Python offers efficient ways to perform stack and queue tasks within a single structure. Another method is using the LifoQueue class to create a stack in Python.<\/p>\n 1. empty():<\/strong> Returns ‘True’ if the stack has no items; otherwise, it returns ‘False’.<\/strong><\/p>\n 2. size():<\/strong> Returns the number of items or elements present in the stack.<\/p>\n 3. top()\/ peek() :<\/strong>\u00a0 Returns a reference to the topmost available element of the stack<\/p>\n 4. push(a):<\/strong> insert the element at the top of the stack<\/p>\n 5. pop():<\/strong> Delete the topmost element of the stack<\/p>\n There are multiple methods to create a stack in Python. This article focuses on building a stack using data structures and modules from the Python library.<\/p>\n Here’s how you can implement a stack in Python:<\/p>\n In Python, you can use the built-in list as a stack. To add items to the top, you use append() instead of push(), and to remove them in a last-in-first-out (LIFO) manner, you use pop().<\/p>\n However, there’s a drawback with using a list: as it grows, it can become slower. This happens because items are stored consecutively in memory. If the stack becomes larger than the current memory block, Python has to allocate more memory, making some append() operations slower than others.<\/p>\n Example<\/strong><\/p>\n Output<\/strong><\/p>\n Initial stack: In Python, you can use the deque class from the collections module to create a stack. Using deque is better than using a list when you want fast add and remove operations from both ends of the stack. This is because deque offers constant-time complexity (O(1)) for these operations, whereas a list has a linear time complexity (O(n)).<\/p>\n The methods used with deque are similar to those with lists: append() and pop().<\/p>\n Example<\/strong><\/p>\n Output<\/strong><\/p>\n Initial stack: The Queue module also provides a Last-In-First-Out (LIFO) Queue, essentially functioning like a Stack. You can add data to this queue using the put() method, while the get() method retrieves data from it.<\/p>\n Several functions are available within this module:<\/p>\n Example<\/strong><\/p>\n Output<\/strong> The linked list provides two methods, addHead(item) and removeHead(), which operate in constant time. These methods are well-suited for implementing a stack.<\/p>\n Example<\/strong><\/p>\n Output<\/strong><\/p>\n My Stack: 10->9->8->7->6->5->4->3->2->1 Stacks in Python offer efficient LIFO operations<\/strong>, with implementations using lists, and collections. deque, and the queue module. While efficient for certain tasks like reversing sequences, they have size limitations and lack direct access beyond the top element.<\/p>\n","protected":false},"author":1,"featured_media":52879,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"","class_list":["post-37168","faq","type-faq","status-publish","has-post-thumbnail","hentry","faq_topics-kb","faq_topics-product-documentation","faq_topics-python-series","faq_topics-python","faq_topics-stack-in-python","faq_topics-tutorial-series","faq_topics-tutorials"],"yoast_head":"\n![\"Stack](\"https:\/\/accuweb.cloud\/resource\/wp-content\/uploads\/2024\/01\/stackpython.png\")
<\/p>\n![\"\"](\"https:\/\/accuweb.cloud\/resource\/wp-content\/uploads\/2024\/01\/stackpython2.png\")
<\/p>\nHow to Create a Stack in Python?<\/h2>\n
Methods of Python Stack<\/h3>\n
\n
Implementation<\/h2>\n
\n
1. Implementation using list<\/h3>\n
\r\n# Python example to\r\n# Show stack using the list\r\nmy_stack = []\r\n# Use append() to add\r\n# items to the stack\r\nmy_stack.append('x')\r\nmy_stack.append('y')\r\nmy_stack.append('z')\r\nprint('Initial stack:')\r\nprint(my_stack)\r\n# Use pop() to remove\r\n# items from the stack\r\nprint('\\nItems removed from the stack:')\r\nprint(my_stack.pop())\r\nprint(my_stack.pop())\r\nprint(my_stack.pop())\r\nprint('\\nStack after removals:')\r\nprint(my_stack)\r\n# Uncommenting print(my_stack.pop())\r\n# will result in an IndexError\r\n# Since the stack is empty<\/code><\/pre>\n
\n[‘x’, ‘y’, ‘z’]
\nItems removed from the stack:
\nz
\ny
\nx
\nStack after removals:
\n[]<\/p>\n2. Implementation using collections.deque<\/h3>\n
\r\n# Python example to\r\n# Illustrate stack using collections.deque\r\nfrom collections import deque\r\nmy_stack = deque()\r\n# Use append() to add\r\n# items to the stack\r\nmy_stack.append('x')\r\nmy_stack.append('y')\r\nmy_stack.append('z')\r\nprint('Initial stack:')\r\nprint(my_stack)\r\n# Use pop() to remove\r\n# items from the stack\r\nprint('\\nItems removed from the stack:')\r\nprint(my_stack.pop())\r\nprint(my_stack.pop())\r\nprint(my_stack.pop())\r\nprint('\\nStack after removals:')\r\nprint(my_stack)\r\n# Uncommenting print(my_stack.pop())\r\n# will lead to an IndexError\r\n# Since the stack is empty<\/code><\/pre>\n
\ndeque([‘x’, ‘y’, ‘z’])
\nItems removed from the stack:
\nz
\ny
\nx
\nStack after removals:
\ndeque([])<\/p>\n3. Implementation using queue module<\/h3>\n
\n
\r\n# Python program to demonstrate stack implementation using the queue module\r\nfrom queue import LifoQueue\r\n# Initializing a stack with a different variable name\r\nmy_stack = LifoQueue(maxsize=3)\r\n# Display the number of elements in the stack using qsize()\r\nprint(my_stack.qsize())\r\n# Add elements to the stack using put()\r\nmy_stack.put('a')\r\nmy_stack.put('b')\r\nmy_stack.put('c')\r\n# Check if the stack is full and display its size\r\nprint(\"Full: \", my_stack.full())\r\nprint(\"Size: \", my_stack.qsize())\r\n# Remove elements from the stack using get() in LIFO order\r\nprint('\\nElements popped from the stack:')\r\nprint(my_stack.get())\r\nprint(my_stack.get())\r\nprint(my_stack.get())\r\n# Check if the stack is empty\r\nprint(\"\\nEmpty: \", my_stack.empty())<\/code><\/pre>\n
\n0
\nFull:\u00a0 True
\nSize:\u00a0 3
\nElements popped from the stack:
\nc
\nb
\na
\nEmpty:\u00a0 True<\/p>\nImplementation using a singly linked list<\/h3>\n
\n
\r\n# Python program to demonstrate stack implementation using a linked list and different variable names.\r\nclass Node:\r\n\u00a0 \u00a0 def __init__(self, data):\r\n\u00a0 \u00a0 \u00a0 \u00a0 self.data = data\r\n\u00a0 \u00a0 \u00a0 \u00a0 self.next = None\r\nclass Stack:\r\n\u00a0 \u00a0 # Initializing the stack with a dummy node for handling edge cases.\r\n\u00a0 \u00a0 def __init__(self):\r\n\u00a0 \u00a0 \u00a0 \u00a0 self.top = Node(\"top_dummy\")\r\n\u00a0 \u00a0 \u00a0 \u00a0 self.count = 0\r\n\u00a0 \u00a0 # String representation of the stack\r\n\u00a0 \u00a0 def __str__(self):\r\n\u00a0 \u00a0 \u00a0 \u00a0 current = self.top.next\r\n\u00a0 \u00a0 \u00a0 \u00a0 representation = \"\"\r\n\u00a0 \u00a0 \u00a0 \u00a0 while current:\r\n\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 representation += str(current.data) + \"->\"\r\n\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 current = current.next\r\n\u00a0 \u00a0 \u00a0 \u00a0 return representation[:-2]\r\n\u00a0 \u00a0 # Obtain the current size of the stack\r\n\u00a0 \u00a0 def getStackSize(self):\r\n\u00a0 \u00a0 \u00a0 \u00a0 return self.count\r\n\u00a0 \u00a0 # Check if the stack is empty\r\n\u00a0 \u00a0 def checkEmpty(self):\r\n\u00a0 \u00a0 \u00a0 \u00a0 return self.count == 0\r\n\u00a0 \u00a0 # Peek at the top item of the stack\r\n\u00a0 \u00a0 def topItem(self):\r\n\u00a0 \u00a0 \u00a0 \u00a0 if self.checkEmpty():\r\n\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 raise Exception(\"Attempting to peek an empty stack\")\r\n\u00a0 \u00a0 \u00a0 \u00a0 return self.top.next.data\r\n\u00a0 \u00a0 # Push a value onto the stack\r\n\u00a0 \u00a0 def pushValue(self, data):\r\n\u00a0 \u00a0 \u00a0 \u00a0 node = Node(data)\r\n\u00a0 \u00a0 \u00a0 \u00a0 node.next = self.top.next\r\n\u00a0 \u00a0 \u00a0 \u00a0 self.top.next = node\r\n\u00a0 \u00a0 \u00a0 \u00a0 self.count += 1\r\n\u00a0 \u00a0 # Remove and retrieve the top item from the stack\r\n\u00a0 \u00a0 def popValue(self):\r\n\u00a0 \u00a0 \u00a0 \u00a0 if self.checkEmpty():\r\n\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 raise Exception(\"Attempting to pop from an empty stack\")\r\n\u00a0 \u00a0 \u00a0 \u00a0 remove_item = self.top.next\r\n\u00a0 \u00a0 \u00a0 \u00a0 self.top.next = self.top.next.next\r\n\u00a0 \u00a0 \u00a0 \u00a0 self.count -= 1\r\n\u00a0 \u00a0 \u00a0 \u00a0 return remove_item.data\r\n# Driver Code\r\nif __name__ == \"__main__\":\r\n\u00a0 \u00a0 my_stack = Stack()\r\n\u00a0 \u00a0 for num in range(1, 11):\r\n\u00a0 \u00a0 \u00a0 \u00a0 my_stack.pushValue(num)\r\n\u00a0 \u00a0 print(f\"My Stack: {my_stack}\")\r\n\u00a0\r\n\u00a0 \u00a0 for _ in range(1, 6):\r\n\u00a0 \u00a0 \u00a0 \u00a0 removed = my_stack.popValue()\r\n\u00a0 \u00a0 \u00a0 \u00a0 print(f\"Removed Item: {removed}\")\r\n\u00a0 \u00a0 print(f\"My Stack: {my_stack}\")<\/code><\/pre>\n
\nRemoved Item: 10
\nRemoved Item: 9
\nRemoved Item: 8
\nRemoved Item: 7
\nRemoved Item: 6
\nMy Stack: 5->4->3->2->1<\/p>\nAdvantages of Stack in Python<\/h3>\n
\n
Disadvantages of Stack in Python<\/h3>\n
\n
Conclusion<\/h2>\n