Examples
Series

In [1]:
import numpy as np
import pandas as pd
In [2]:
s = pd.Series([3, np.nan, 4, -5, 0])
s
Out[2]:
0    3.0
1    NaN
2    4.0
3   -5.0
4    0.0
dtype: float64

By default, NA values are ignored.

In [3]:
s.cumsum()
Out[3]:
0    3.0
1    NaN
2    7.0
3    2.0
4    2.0
dtype: float64

To include NA values in the operation, use skipna=False

In [4]:
s.cumsum(skipna=False)
Out[4]:
0    3.0
1    NaN
2    NaN
3    NaN
4    NaN
dtype: float64