如何计算自列标志起的天数?

我有一个如下定义的数据帧。我想数一数 input 列从1更改为0:

import pandas as pd
df = pd.DataFrame({'input': [1,1,1,0,0,0,1,1,1,0,0,0]}, 
                  index=pd.date_range('2021-10-01', periods=12))
# I can mark the points of interest, i.e. when it goes from 1 to 0
df['change'] = 0
df.loc[(df['input'].shift(1) - df['input']) > 0, 'change'] = 1
print(df)

            input   change
2021-10-01      1        0
2021-10-02      1        0 
2021-10-03      1        0
2021-10-04      0        1
2021-10-05      0        0
2021-10-06      0        0
2021-10-07      1        0
2021-10-08      1        0
2021-10-09      1        0
2021-10-10      0        1
2021-10-11      0        0
2021-10-12      0        0

我想要的是一个 res 输出:

            input   change     res
2021-10-01      1        0       0
2021-10-02      1        0       0  
2021-10-03      1        0       0
2021-10-04      0        1       1
2021-10-05      0        0       2
2021-10-06      0        0       3
2021-10-07      1        0       0
2021-10-08      1        0       0
2021-10-09      1        0       0
2021-10-10      0        1       1
2021-10-11      0        0       2
2021-10-12      0        0       3

cumsum 但没有找到在适当的点“重置它”的方法:

df['res'] = (1 - df['input']).cumsum()*(1 - df['input'])

但上述情况将继续累积,而不会在何处重置 change == 1