# if you want to fill NaN in a single column with its mean value
df['col'].fillna(df['col'].mean(), inplace=True)
# if you want to fill NaN in more than one columns with their respective mean values
df.fillna(df.mean(), inplace=True)
# if you want to fill NaN in a single column with its mean value
df['col'].fillna(df['col'].mean(), inplace=True)
# if you want to fill NaN in more than one columns with their respective mean values
df.fillna(df.mean(), inplace=True)