Step 3: Summarise: totals and regions

Now answer the first questions: total revenue, units, the average order, and revenue by region. Group with a dictionary: for each sale, add its revenue to the entry for its region. Then sort the regions from best to worst.

Examplepython

import csv, io

RAW = """date,region,product,units,price
2026-01-05,North,Notebook,10,4.50
2026-01-09,South,Pen,50,1.20
2026-01-12,North,Backpack,3,39.90
2026-01-15, East ,Notebook,8,4.50
2026-02-01,South,Headphones,2,59.00
2026-02-03,West,Pen,n/a,1.20
2026-02-10,North,Pen,40,1.20
2026-02-14,East,Backpack,5,39.90
2026-02-20,,Mouse,4,19.50
2026-03-02,South,Notebook,12,4.50
2026-03-09,West,Headphones,3,59.00
2026-03-15,North,Mouse,6,19.50
2026-03-21,East,Pen,30,1.20"""

def clean(raw_rows):
    good = []
    for r in raw_rows:
        try:
            units, price = int(r["units"]), float(r["price"])
        except ValueError:
            continue
        if not r["region"].strip():
            continue
        good.append({"date": r["date"], "region": r["region"].strip(), "product": r["product"].strip(),
                     "units": units, "price": price, "revenue": round(units * price, 2)})
    return good

sales = clean(csv.DictReader(io.StringIO(RAW)))

total = sum(s["revenue"] for s in sales)
print("total revenue:", round(total, 2))
print("units sold:", sum(s["units"] for s in sales))
print("average order:", round(total / len(sales), 2))

by_region = {}
for s in sales:
    by_region[s["region"]] = by_region.get(s["region"], 0) + s["revenue"]
for region, revenue in sorted(by_region.items(), key=lambda kv: kv[1], reverse=True):
    print(f"{region:<6} {revenue:>8.2f}")

Open in editor »

You should see that North earns the most. The format spec {revenue:>8.2f} means: right-aligned, 8 characters wide, 2 decimals, which makes the columns line up.

Your turn: write the code

Given the list of (region, revenue) pairs, build a dictionary of total revenue per region and print the total for "North" and for "South".

Quick check

How does the code add revenue to a region it has not seen yet?

dict.get(key, 0) supplies a starting value of 0It raises an errorIt skips the region

Finish the quick check (and any code exercise) to complete this lesson, or mark it done yourself.

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