Replace values from second row onwards in a pandas pipe method

I am wondering how to replace values from second row onwards in a pipe method (connecting to the rest of steps).

import pandas as pd
import numpy as np

df = pd.DataFrame(
    {
        "Date": ["2020-01-01", "2021-01-01", "2022-01-01"],
        "Pop": [90, 70, 60],
    }
)

         Date  Pop
0  2020-01-01   90
1  2021-01-01   70
2  2022-01-01   60

Current solution

df.iloc[1:] = np.nan

Expected output

         Date  Pop
0  2020-01-01   90
1  2021-01-01  NaN
2  2022-01-01  NaN

>Solution :

You can also use assign like this:

df.assign(Pop=df.loc[[0], 'Pop'])

Output:

         Date   Pop
0  2020-01-01  90.0
1  2021-01-01   NaN
2  2022-01-01   NaN

Note: assign works with nice column headers, if your headers have spaces or special characters you will need to use a different method.