script_3.py - List as Stack (LIFO)

Code

See script_3.py for full code.

Explanation

Line 8: class BrowserHistory: - Defines a class (custom type) - Classes group related data and functions

Line 9: def __init__(self): - __init__ is constructor method (called when object created) - self is reference to instance - Initializes object state

Line 10: self.history = [] - Instance variable (belongs to this object) - Empty list to store history stack - self. prefix makes it accessible across methods

Line 11: self.current = None - None is Python's null/empty value - Represents no current page

Line 18: self.history.append(self.current) - .append() adds to end of list (push operation) - Stack grows at the end - LIFO: Last In, First Out

Line 25: previous = self.history.pop() - .pop() without argument removes and returns last element - Stack shrinks from the end - Reverses the append order - List must not be empty (checked with if self.history)

Line 27: self.current = previous - Updates current page to popped value - Simulates going back in browser