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Ex 18: Parcel Scanning System

Problem​

Automate a parcel scanning system for a warehouse. We need to process a list of barcodes and handle damaged items or critical errors.

Rules​

  • Define scan_parcels(parcel_codes: list[str]) -> list[str].
  • If a barcode is "DAMAGED", skip it and log "Skipped damaged parcel".
  • If a barcode is "STOP", exit immediately and log "Critical error: Stopping scan".
  • Use a for-else block to log "All parcels scanned successfully" only if the scan was not stopped.

Boilerplate​

Copy below code and paste to our IDE for head start.

# Write our code inside this function
def scan_parcels(parcel_codes: list[str]) -> list[str]:
    pass # remove this

# Call with test data
print(scan_parcels(["ABC", "DAMAGED", "XYZ"]))

Expected Output​

['Scanned parcel: ABC', 'Skipped damaged parcel', 'Scanned parcel: XYZ', 'All parcels scanned successfully']

Solution​

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Show solution
def scan_parcels(parcel_codes: list[str]) -> list[str]:
    messages: list[str] = []

    for barcode in parcel_codes:
        if barcode.lower() == "damaged":
            messages.append("Skipped damaged parcel")
            continue
        elif barcode.lower() == "stop":
            messages.append("Critical error: Stopping scan")
            break
        else:
            messages.append(f"Scanned parcel: {barcode}")
    else:
        # Loop finished without hitting "STOP"
        messages.append("All parcels scanned successfully")

    return messages

# Test call
print(scan_parcels(["ABC", "DAMAGED", "XYZ"]))

Details​

The for-else block is the cleanest way to handle the "all successful" message. It avoids the need for a boolean flag (like was_stopped = False) to check if the loop was interrupted by the break statement.