如何使用pandas计算库存何时耗尽？

import pandas as pd

# 准备数据
data = {
    '日期': pd.date_range(start='2022-01-01', end='2022-01-31'),
    '产品A库存': [100, 90, 80, 70, 60, 50, 40, 30, 20, 10, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0],
    '产品B库存': [200, 190, 180, 170, 160, 150, 140, 130, 120, 110, 100, 90, 80, 70, 60, 50, 40, 30, 20, 10, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]
}

df = pd.DataFrame(data)

# 计算每日销售量
df['产品A销售量'] = df['产品A库存'].diff().fillna(df['产品A库存'])
df['产品B销售量'] = df['产品B库存'].diff().fillna(df['产品B库存'])

# 计算库存耗尽时间
df['产品A耗尽天数'] = df['产品A库存'] / df['产品A销售量']
df['产品B耗尽天数'] = df['产品B库存'] / df['产品B销售量']

# 可视化结果
df.plot(x='日期', y=['产品A耗尽天数', '产品B耗尽天数'], marker='o')