Greetings! Today, we're drawing back the curtains on Stacks in Python, a crucial data structure. A stack is like a pile of dishes: you add a dish to the top (Last In) and take it from the top (First Out). This Last-In, First-Out (LIFO) principle exemplifies the stack. Python executes stacks effortlessly using Lists. This lesson will illuminate the stack data structure, operations, and their Python applications. Are you ready to start?

A stack is an elongated storehouse permitting Push (addition) and Pop (removal) operations. It's akin to a stack of plates in a cafeteria where plates are added (pushed) and removed (popped) from the top. No plate can be taken from the middle or the bottom, exemplifying a Last-In, First-Out (LIFO) operation.

To create a stack, Python employs a built-in data structure known as a List. For the Push operation, we use append(), which adds an element at the list's end. For the Pop operation, there's the pop() function that removes the last element, simulating the removal of the 'top' element in a stack. Here's how it looks:

stack = [] # A new empty stack

# Push operations
stack.append('John')
stack.append('Mary')
stack.append('Steve')

stack.pop() # Pop operation removes 'Steve'
print(stack) # Outputs: ['John', 'Mary']

In the example provided, we push 'John', 'Mary', and 'Steve' into the stack and then pop 'Steve' from the stack.

Stacks operations go beyond merely push and pop. For example, to verify if a stack is empty, we can use the len() function. If it returns 0, that means the stack is empty. Conversely, if it returns a nonzero value, we can infer the stack is not empty. To peek at the top element of the stack without popping it, merely indexing with -1 is handy.

Here's an example:

stack.append('Sam')
print(stack[-1]) # Outputs: 'Sam'

In this example, 'Sam' is added (pushed), and then the topmost stack element, which is 'Sam', is peeked.

Practical applications of stacks in Python are plentiful. Here is one of them - reversing a string.

We will push all characters into a stack and then pop them out to get a reversed string!

def reverse_string(input_string):
    stack = list(input_string)
    
    reversed_string = ''
    while len(stack) > 0:
        reversed_string += stack.pop()
    return reversed_string

print(reverse_string('HELLO')) # Outputs: OLLEH