How to apply fillna to last N columns of a pandas dataframe?

Question

I have a data frame with many columns. I would like to fill the nan's with 0's for the last x number of columns. I used the following code but it doesn't seem to work.

df.iloc[:, -10:-1].fillna(value=0, inplace=True)

What am I doing wrong? when I specifically refer to a column by name:

df['column_a'].fillna(value=0, inplace=True)

it works, but I'd rather not do it one column at a time.

Answer 1

A recipe that should work here is

df.iloc[:, -x:] = df.iloc[:, -x:].fillna(value=0)

A reproducible example here is

import pandas as pd
df = pd.DataFrame({'col1':range(10),
                   'col2':range(1, 11), 
                   'col3':range(2, 12),
                   'col4':range(3, 13),
                   'col5':range(4, 14)})

# pepper with NaNs
df.iloc[8, 2] = None
df.iloc[8, 3] = None
df.iloc[8, 4] = None

# apply fillna change to last 2 cols
x = 2
df.iloc[:, -x:] = df.iloc[:, -x:].fillna(value=0)

print(df)