Замените NAN в столбце Pandas режимом и печатайте его
def exercise4(df):
df1 = df.select_dtypes(np.number)
df2 = df.select_dtypes(exclude = 'float')
mode = df2.mode()
df3 = df1.fillna(df.mean())
df4 = df2.fillna(mode.iloc[0,:])
new_df = [df3,df4]
df5 = pd.concat(new_df,axis=1)
new_cols = list(df.columns)
df6 = df5[new_cols]
return df6
Grieving Giraffe