Implement a user-defined function extend_df that takes a data frame df as the input argument and returns another data frame df_out that satisfies the following conditions.

If the dimension of df is , then the dimension of df_out is (+2)(+2).

Every entry of the first and the last rows of df_out is NaN.

Every entry of the first and the last columns of df_out is NaN.

Other entries are identical to df. More precisely, df_out.iloc[1:(r+1),1:(c+1)] is equal to df.

def extend_df(df): import pandas as pd import numpy as np r = ????? c = ????? # Initializing df_out as a (r+2)x(c+2) dataframe of "np.nan"s df_out = pd.?????(np.nan, index=range(?????), columns=range(?????)) for i in range(r): for j in range(c): # The (i+1, j+1) component of "df_out" equals the (i,j) component of "df" df_out.?????[?????,?????] = df.?????[?????,?????] return(df_out)