Mini project: a monthly sales report

# daily_sales_report.py: only the basics from Lessons 1 to 18

def read_orders(path):
    """Read orders.csv into a list of dicts."""
    rows = []
    with open(path) as f:
        header = f.readline().strip().split(",")
        for line in f:
            values = line.strip().split(",")
            rows.append(dict(zip(header, values)))
    return rows

def month_of(day):
    return day[:7]                                   # "2025-04-20" -> "2025-04"

def build_report(rows):
    report = {}
    for r in rows:
        if r["status"] != "delivered":
            continue
        month = month_of(r["order_date"])
        if month not in report:
            report[month] = {"orders": 0, "revenue": 0.0, "best": 0.0}
        stats = report[month]
        amount = float(r["amount"])
        stats["orders"] += 1
        stats["revenue"] += amount
        if amount > stats["best"]:
            stats["best"] = amount
    return report

def print_report(report):
    print(f"{'month':<9}{'orders':>7}{'revenue':>11}{'average':>10}{'best':>9}")
    print("-" * 46)
    grand = 0.0
    for month in sorted(report):
        s = report[month]
        avg = s["revenue"] / s["orders"]
        grand += s["revenue"]
        print(f"{month:<9}{s['orders']:>7}{s['revenue']:>11,.2f}{avg:>10,.2f}{s['best']:>9,.0f}")
    print("-" * 46)
    print(f"{'total':<9}{'':>7}{grand:>11,.2f}")

rows = read_orders("orders.csv")
print(len(rows), "orders read")
print_report(build_report(rows))

15 orders read
month     orders    revenue   average     best
----------------------------------------------
2025-01        2   1,994.00    997.00    1,198
2025-02        2   2,847.00  1,423.50    1,499
2025-03        4   7,291.00  1,822.75    3,498
2025-04        4   6,840.00  1,710.00    2,397
----------------------------------------------
total             18,972.00