Python | 標準ライブラリ（csv + pathlib + collections + datetime）だけ を使って、「商品ごとに売上トップの月を抽出」する実践例

import csv
from pathlib import Path
from collections import defaultdict
from datetime import datetime

csv_path = Path.home() / "Documents" / "sales.csv"

# 集計用: {月: {商品: 金額合計}}
summary = defaultdict(lambda: defaultdict(int))

with csv_path.open("r", encoding="utf-8") as f:
    reader = csv.DictReader(f)
    for row in reader:
        date = datetime.strptime(row["日付"], "%Y-%m-%d")
        month = date.strftime("%Y-%m")  # "2025-11" のように月単位にまとめる
        product = row["商品"]
        price = int(row["金額"])
        summary[month][product] += price

# 月ごとにランキングを表示
for month, products in sorted(summary.items()):
    print(f"=== {month} の売上ランキング ===")
    # 金額で降順ソート
    ranking = sorted(products.items(), key=lambda x: x[1], reverse=True)
    for rank, (product, total) in enumerate(ranking, start=1):
        print(f"{rank}位: {product} - {total}円")
    print()

import csv
from pathlib import Path
from collections import defaultdict
from datetime import datetime

csv_path = Path.home() / "Documents" / "sales.csv"

# 集計用: {月: {商品: 金額合計}}
summary = defaultdict(lambda: defaultdict(int))

with csv_path.open("r", encoding="utf-8") as f:
    reader = csv.DictReader(f)
    for row in reader:
        date = datetime.strptime(row["日付"], "%Y-%m-%d")
        month = date.strftime("%Y-%m")  # "2025-11" のように月単位にまとめる
        product = row["商品"]
        price = int(row["金額"])
        summary[month][product] += price

# 月ごとにランキングを表示
for month, products in sorted(summary.items()):
    print(f"=== {month} の売上ランキング ===")
    # 金額で降順ソート
    ranking = sorted(products.items(), key=lambda x: x[1], reverse=True)
    for rank, (product, total) in enumerate(ranking, start=1):
        print(f"{rank}位: {product} - {total}円")
    print()