Project — A Receipt Formatter

By the end of this lesson you can:

• Turn a list of messy order lines into a clean, aligned receipt.
• Skip a bad line and report it, instead of crashing on it.
• Combine split, strip, title, validation and f-string widths in one program.

Here is the data the program will receive. Before writing anything, read it and list what is wrong with each line.

orders.txt, as typed

pizza, 2, 3.50
  HOT CHOCOLATE ,3, 2.50
pancake,1,2.00
noodles
ice cream, two, 4.90
hot dog,10,1.20  

Every program in this section has had the same three stages. Naming them makes the project straightforward rather than daunting.

The pipeline

  PARSE            CHECK             FORMAT
  split the line   is it usable?     build the row
  strip each part  skip if not       align the columns
  fix the case     convert numbers   add up the total

• Parse — lesson 3 (split) and lesson 2 (strip, title).
• Check — lesson 5 (len() of the split, isdigit()).
• Format — lesson 4 (f-string widths and :.2f).

Keeping the stages separate is what makes the program readable. Parse everything first, then check, then format — rather than doing all three inside one tangled loop.

# One line, through all three stages

raw = "  HOT CHOCOLATE ,3, 2.50"

# PARSE
fields = raw.split(",")
name = fields[0].strip().title()
qty_text = fields[1].strip()
price_text = fields[2].strip()

# CHECK
if qty_text.isdigit():
    qty = int(qty_text)
    price = float(price_text)

    # FORMAT
    print(f"{name:<18}{qty:>4}{price * qty:>9.2f}")

Output

Hot chocolate            3     7.50

Type it in four goes, running it after each one. Do not paste the whole thing.

Step 1 — the data and the header

# receipt.py - messy order lines in, a tidy receipt out

STALL = "Food stall Pak Din"
orders = [
    "pizza, 2, 3.50",
    "  HOT CHOCOLATE ,3, 2.50",
    "pancake,1,2.00",
    "noodles",
    "ice cream, two, 4.90",
    "hot dog,10,1.20  ",
]

header = f"{'Item':<18}{'Qty':>4}{'Unit':>9}{'Total':>10}"
print(STALL.center(len(header)))
print("=" * len(header))
print(header)
print("-" * len(header))

center() is new — it pads both sides so the stall name sits in the middle of the receipt. Run it: you should see a heading and two rules, no rows yet.

Step 2 — parse and check each line

rejected = []
grand_total = 0

for raw in orders:
    fields = raw.split(",")

    if len(fields) != 3:
        rejected.append(raw.strip())
        continue

    name = fields[0].strip().title()
    qty_text = fields[1].strip()
    price_text = fields[2].strip()

    if not qty_text.isdigit():
        rejected.append(raw.strip())
        continue

    if not price_text.replace(".", "", 1).isdigit():
        rejected.append(raw.strip())
        continue

continue abandons this line and moves to the next. Each check runs before the conversion it protects — that is the whole trick.

Step 3 — format the row

    qty = int(qty_text)
    unit = float(price_text)
    line_total = qty * unit
    grand_total = grand_total + line_total

    print(f"{name:<18}{qty:>4}{unit:>9.2f}{line_total:>10.2f}")

Step 4 — the total and the rejects

print("-" * len(header))
print(f"{'GRAND TOTAL':<18}{'':>4}{'':>9}{grand_total:>10.2f}")
print("=" * len(header))

if rejected:
    print()
    print(f"{len(rejected)} line(s) could not be read:")
    for bad in rejected:
        print(f"   {bad!r}")

print()
print("Thank you!".center(len(header)))

Output

             Food stall Pak Din
=========================================
Item                Qty     Unit     Total
-----------------------------------------
Pizza            2     3.50      7.00
Hot chocolate             3     2.50      7.50
Pancake            1     2.00      2.00
Hot dog                10     1.20     12.00
-----------------------------------------
GRAND TOTAL                          28.50
=========================================

2 line(s) could not be read:
   'noodles'
   'ice cream, two, 4.90'

              Thank you!

Four good rows, two reported, one correct total, and nothing crashed. The person at the stall can see exactly which two lines to retype.

Six lessons, and this project used all of them. Strings are rows of characters you can index and slice; methods hand back tidy copies rather than changing the original; split and join move between text and lists; f-strings build output that lines up; and asking a string what it contains before converting it is what stops programs crashing on real typing.

Where next. Section 7 · Errors & Debugging replaces the isdigit guards with try / except, which handles decimals properly and reads better. Section 2 · Lists goes deeper into the list that split hands you.