To prepare a dataframe with elements being repeated from a list in python - pandas

Question

I have a list as primary = ['A' , 'B' , 'C' , 'D']
and a DataFrame as
df2 = pd.DataFrame(data=dateRange, columns = ['Date'])
which contains 1 date column starting from 01-July-2020 till 31-Dec-2020.
I created another column 'DayNum' which will contain the day number from the date like 01-July-2020 is Wednesday so the 'DayNum' column will have 2 and so on.
Now using the list I want to create another column 'primary' so that the DataFrame looks as follows:
In short, the elements on the list should repeat. You can say that this is a roster to show the name of the person on the roster on a weekly basis where Monday is the start (day 0) and Sunday is the end (day 6).
The output should be like this:
Date DayNum Primary
0 01-Jul-20 2 A
1 02-Jul-20 3 A
2 03-Jul-20 4 A
3 04-Jul-20 5 A
4 05-Jul-20 6 A
5 06-Jul-20 0 B
6 07-Jul-20 1 B
7 08-Jul-20 2 B
8 09-Jul-20 3 B
9 10-Jul-20 4 B
10 11-Jul-20 5 B
11 12-Jul-20 6 B
12 13-Jul-20 0 C
13 14-Jul-20 1 C
14 15-Jul-20 2 C
15 16-Jul-20 3 C
16 17-Jul-20 4 C
17 18-Jul-20 5 C
18 19-Jul-20 6 C
19 20-Jul-20 0 D
20 21-Jul-20 1 D
21 22-Jul-20 2 D
22 23-Jul-20 3 D
23 24-Jul-20 4 D
24 25-Jul-20 5 D
25 26-Jul-20 6 D
26 27-Jul-20 0 A
27 28-Jul-20 1 A
28 29-Jul-20 2 A
29 30-Jul-20 3 A
30 31-Jul-20 4 A

Answer 1

First compare column for 0 by Series.eq with cumulative sum by Series.cumsum for groups for each week, then use modulo by Series.mod with number of values in list and last map by dictioanry created by enumerate and list by Series.map:
primary = ['A','B','C','D']
d = dict(enumerate(primary))
df['Primary'] = df['DayNum'].eq(0).cumsum().mod(len(primary)).map(d)