Create a new row for each day (pd.date_range) - Merge, Join or Concat?

I'm trying to create a dataframe by "multiplying" two others. Let me show you what I've tried to do.

1 - Create a dataframe from a data range

df_dates = pd.DataFrame({'date_prediciton':pd.date_range(start='2021-08-01', end='2021-08-31', freq='W-SUN')})
df_dates.head()
    date_prediciton
0   2021-08-01
1   2021-08-08
2   2021-08-15
3   2021-08-22
4   2021-08-29

2 - Create a dataframe of clients

client = ['101', '102', '103', '104']
df_clients = pd.DataFrame(data=client, columns=['client'])
df_clients.head()

client
0   101
1   102
2   103
3   104

3 - Then a need to "multiply" (this may not be the right expression), each client to the date range

Solution

You can use pd.MultiIndex.from_product to create cartesian product of the two:

print (pd.MultiIndex.from_product([client, df_dates["date_prediciton"]]).to_frame(index=0, name=["client", "date"]))

   client       date
0     101 2021-08-01
1     101 2021-08-08
2     101 2021-08-15
3     101 2021-08-22
4     101 2021-08-29
5     102 2021-08-01
6     102 2021-08-08
7     102 2021-08-15
8     102 2021-08-22
9     102 2021-08-29
10    103 2021-08-01
11    103 2021-08-08
12    103 2021-08-15
13    103 2021-08-22
14    103 2021-08-29
15    104 2021-08-01
16    104 2021-08-08
17    104 2021-08-15
18    104 2021-08-22
19    104 2021-08-29