Lecture: Hands-on with Stacks and Queues in Python

Overview

• Focus: Hands-on demonstration of stacks and queues using Python.
• Goal: Show how to use built-in Python data structures to implement stacks and queues.

Stacks

• Data Structure Used: List
• Key Operations:
  • Push: data.append(element)
  • Pop: element = data.pop()
• Additional Operation:
  • Peek: element = data[len(data) - 1]
• Behavior: LIFO (Last In First Out)
• Example:

  data = []
  data.append(5)
  element = data.pop()
  print(element)  # Output: 5
  print(data)  # Output: []
  

• Notes:
  • Limit to append and pop to maintain stack integrity.
  • Peek operation: element = data[len(data) - 1]
  • Visual example with multiple operations for better understanding.

Queues

• Data Structure Used: List
• Key Operations:
  • Enqueue: data.append(element)
  • Dequeue: element = data.pop(0)
• Additional Operation:
  • Peek: element = data[0]
• Behavior: FIFO (First In First Out)
• Example:

  data = []
  data.append(5)
  data.append(10)
  element = data.pop(0)
  print(element)  # Output: 5
  print(data)  # Output: [10]
  

• Notes:
  • Dequeue operation: element = data.pop(0)
  • Peek operation: element = data[0]
  • Consider performance impact for large lists (O(n) complexity).

Using deque from collections

• Purpose: Optimize pop left operation.
• Import: from collections import deque
• Operations:
  • Append: data.append(element)
  • Pop Left: element = data.popleft()
• Example:

  from collections import deque
  data = deque()
  data.append('Caleb')
  element = data.popleft()
  print(element)  # Output: Caleb
  print(data)  # Output: deque([])
  

• Notes: Efficient for queue operations.

Custom Classes for Stacks and Queues

• Purpose: Strict control over operations and extendibility.
• Example - Custom Stack Class:

  class Stack:
      def __init__(self):
          self._data = []
      def push(self, data):
          self._data.append(data)
      def pop(self):
          return self._data.pop()
      def peek(self):
          return self._data[len(self._data) - 1]
  

• Usage:

  stack = Stack()
  stack.push(10)
  print(stack.peek())  # Output: 10
  print(stack.pop())  # Output: 10
  

• Notes:
  • Use underscores for private variables to discourage direct access.
  • Flexibility to add custom logic or enforce rules.
  • Extend for other data structures like queues or priority queues.

Takeaway

• Adapt these concepts to other programming languages for practice.
• Use built-in structures but also learn to implement custom classes for full control.

Next Steps: Continue to practice with hands-on examples and build a deeper understanding of data structures.