Pandas Forward Fill NA only between two points and nothing else

Question

I want to use pandas forward fill null values only between two non-null data points and nothing else.

For example I have a column named comments

Comments:
Hello World
NA
Hello World
NA 
Hello World
NA
NA
NA
NA

Output should look like this:

Hello World
Hello World
Hello World
Hello World
Hello World
NA
NA
NA
NA

Answer 1

You can calculate the last valid index and use ffill until this index:

last = df['Comments'].last_valid_index()

df['Comments'].loc[:last] = df['Comments'].loc[:last].ffill()

print(df)

      Comments
0  Hello World
1  Hello World
2  Hello World
3  Hello World
4  Hello World
5          NaN
6          NaN
7          NaN
8          NaN