Price After Discount Exercise

Inside the directory you created for this course on Python, create a new folder called Exercise-12-Price-After-Discount and put the .py solution files for this exercise within it.

Before beginning to code anything, let's first settle on what would be required to solve this exercise. It's always a good idea to plan things out before moving over to the code.

So we need to display a row for each item in the given list items.

What does this remind of?

Yup, you're right! We need a for loop. The loop would iterate over items, and for each of its items, execute a piece of code. This piece of code would be responsible to output a row for the given item.

But before this, we'd need to output the headings of the table — they have to be output once so likewise the corresponding code won't go inside the loop.

Let's get done with the headings, to start with:

items = [(50, 30), (85, 10), (300, 15), (20, 5)]

print('Price'.ljust(20) + 'Discount'.ljust(20) + 'Price after discount'.ljust(20))
print()

Notice how we are merely repeating 20 over here. If ever in the future, we feel the need to change this value to 25, or 30, or any other value, we'd have to manually change all the respective values. As you would agree, this is inefficient and inflexible.

A better option is to use a variable to represent the column length and use that variable instead of 20 in the string padding methods.

So, let's make this change in our code:

items = [(50, 30), (85, 10), (300, 15), (20, 5)]
col_len = 20

print('Price'.ljust(col_len) + 'Discount'.ljust(col_len) + 'Price after discount'.ljust(col_len))
print()

Moving on, the next step is to output the rest of the table. For each item in items, there has to be a row output to the shell.

The logic for this part would obviously go inside the loop.

To start with, we'll retrieve the actual price and discount of the current item in the loop in the variables price and discount, respectively and then compute the final price after applying the discount. The result will be saved inside a variable final_price:

items = [(50, 30), (85, 10), (300, 15), (20, 5)]
col_len = 20

print('Price'.ljust(col_len) + 'Discount'.ljust(col_len) + 'Price after discount'.ljust(col_len))
print()

for item in items:
    price = item[0]
    discount = item[1]
    final_price = price - (price * discount / 100)

Once done, we'll round both price and final_price to 2 decimal places (using the format() method), add the '$' sign at the start, and assign the result back to each respective variable:

items = [(50, 30), (85, 10), (300, 15), (20, 5)]
col_len = 20

print('Price'.ljust(col_len) + 'Discount'.ljust(col_len) + 'Price after discount'.ljust(col_len))
print()

for item in items:
    price = item[0]
    discount = item[1]
    final_price = price - (price * discount / 100)

    price = '$' + '{:.2f}'.format(price)
    final_price = '$' + '{:.2f}'.format(final_price)

Next, we'll convert discount to a string using str() and add the '%' sign at its end:

items = [(50, 30), (85, 10), (300, 15), (20, 5)]
col_len = 20

print('Price'.ljust(col_len) + 'Discount'.ljust(col_len) + 'Price after discount'.ljust(col_len))
print()

for item in items:
    price = item[0]
    discount = item[1]
    final_price = price - (price * discount / 100)

    price = '${:.2f}'.format(price)
    final_price = '${:.2f}'.format(final_price)
    discount = str(discount) + '%'

The last step is to pad each of these strings to col_len, concatenate them all and print the final string to the shell:

items = [(50, 30), (85, 10), (300, 15), (20, 5)]
col_len = 20

print('Price'.ljust(col_len) + 'Discount'.ljust(col_len) + 'Price after discount'.ljust(col_len))
print()

for item in items:
    price = item[0]
    discount = item[1]
    final_price = price - (price * discount / 100)

    price = '${:.2f}'.format(price)
    final_price = '${:.2f}'.format(final_price)
    discount = str(discount) + '%'

    print(price.ljust(col_len) + discount.ljust(col_len) + final_price.ljust(col_len))

This completes our exercise.