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: {商品: {月: 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[product][month] += price

# 商品ごとに売上トップの月を抽出
for product, months in summary.items():
    # 最大金額の月を探す
    top_month, top_sales = max(months.items(), key=lambda x: x[1])
    print(f"{product}: 売上トップの月 = {top_month}, 金額 = {top_sales}")

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

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

# 集計用: {商品: {月: 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[product][month] += price

# 商品ごとに売上トップの月を抽出
for product, months in summary.items():
    # 最大金額の月を探す
    top_month, top_sales = max(months.items(), key=lambda x: x[1])
    print(f"{product}: 売上トップの月 = {top_month}, 金額 = {top_sales}")