Question

A stack named FruitStack, implemented using list, contains records of some fruits. Each record is represented as a dictionary with keys 'Name', 'Origin', 'Price', and 'Expiry'. A sample record is given here:

{'Name':'Apple','Origin':'France','Price':120,'Expiry':'12-08-2025'}

Write the following user-defined functions in Python to perform the specified operations on FruitStack:

(i) push_fruit(FruitStack, Fruit): This function takes the stack FruitStack and a new record Fruit as arguments and pushes the record stored in Fruit onto FruitStack if the Price is less than 100.

(ii) pop_fruit(FruitStack): This function pops the topmost record from the stack and returns it. If the stack is already empty, the function should display “UNDERFLOW”.

(iii) display(FruitStack): This function displays all the elements of the stack starting from the topmost element. If the stack is empty, the function should display 'EMPTY STACK'.

Hint:

Use append() for push when Price is below 100, pop() with an emptiness check, and a loop from the last index to 0 for display.

Answer 1

Step 1: Understand the stack:
A stack follows the LIFO rule: last in, first out. We use a list, and the end of the list is the top of the stack.
Push means append() at the end. Pop means pop() from the end.

Step 2: Write push_fruit():
The record is pushed only if its Price is less than 100. So we test the 'Price' key first.

def push_fruit(FruitStack, Fruit):
    if Fruit['Price'] < 100:
        FruitStack.append(Fruit)

A record with Price 120, like the Apple record, is not pushed.

Step 3: Write pop_fruit():
Before popping, we must check that the stack has some element. If it is empty, we display UNDERFLOW. Otherwise we remove and return the top record.

def pop_fruit(FruitStack):
    if len(FruitStack) == 0:
        print('UNDERFLOW')
    else:
        return FruitStack.pop()

Step 4: Write display():
The topmost element is the last item of the list. So we start from the last index and go down to index 0.

def display(FruitStack):
    if len(FruitStack) == 0:
        print('EMPTY STACK')
    else:
        for i in range(len(FruitStack) - 1, -1, -1):
            print(FruitStack[i])

Step 5: Test the functions:
I tested them with three records. The Apple record (Price 120) was not pushed. The Kiwi (90) and Pear (60) records were pushed. display() printed Pear first and then Kiwi. pop_fruit() returned the Pear record. On an empty stack, display() printed EMPTY STACK and pop_fruit() printed UNDERFLOW.

Final Answer:
The three functions above push only records with Price below 100, pop the top record with an UNDERFLOW check, and display from the top.