如何在新创建的文件中获取月份总数？

import csv

# 创建一个新文件，并写入日期数据
with open('dates.csv', 'w', newline='') as file:
    writer = csv.writer(file)
    writer.writerow(['2022-01-01'])
    writer.writerow(['2022-02-01'])
    writer.writerow(['2022-02-15'])
    writer.writerow(['2022-03-01'])
    writer.writerow(['2022-04-01'])
    writer.writerow(['2022-04-15'])

# 读取文件中的日期数据，并提取月份
months = set()
with open('dates.csv', 'r') as file:
    reader = csv.reader(file)
    for row in reader:
        date = row[0]
        month = date.split('-')[1]
        months.add(month)

# 统计月份总数
total_months = len(months)
print("月份总数：", total_months)