Add the missing numbers in the table in order

Question

I need modify a csv file with pandas. I have the following table:

Interface   Description
1           Used
2           Used
3           Used
4           Used
6           Used
8           Used
12          Used
17          Used

I need to match the "Interface" column with a range of 1, 20, complete the table with the missing numbers and place the word "free" in the "Description" column and order it like this:

Interface   Description
1           Used
2           Used
3           Used
4           Used
5           free
6           Used
7           free
8           Used
9           free
10          free
11          free
12          Used
13          free
14          free
15          free
16          free
17          Used
18          free
19          free
20          free

Answer 1

Use merge in combination with fillna

df = pd.DataFrame({
    'Interface': [1, 2, 3, 4, 6, 8, 12, 17],
    'Description': 'Used'})
df2 = pd.DataFrame({'Interface': range(1, 21)}).merge(df, how="left").fillna("free")