python - How to add rows for a timeseries dataframe?

Question

I am writing a program that will load in a timeseries excel file into a dataframe, then I create several new columns using some basic calculations. My program is going to sometimes read in excel files that are missing months for some records. So in example below I have monthly sales data for two different stores. The stores open during different months, so their first month-end date will differ. But both should have month end data up until 9/30/2020. In my file, Store BBB has no records for 8/31/2020 and 9/30/2020 because there were no Sales during those months.

Store	Month Opened	State	City	Month End Date	Sales
AAA	5/31/2020	NY	New York	5/31/2020	1000
AAA	5/31/2020	NY	New York	6/30/2020	5000
AAA	5/31/2020	NY	New York	7/30/2020	3000
AAA	5/31/2020	NY	New York	8/31/2020	4000
AAA	5/31/2020	NY	New York	9/30/2020	2000
BBB	6/30/2020	CT	Hartford	6/30/2020	100
BBB	6/30/2020	CT	Hartford	7/30/2020	200

Answer 1

1. just try upsample of the DateTime index. ref: pandas-resample-upsample-last-date-edge-of-data

# group by `Store`
# with `Month End Date` column show be converted to DateTime

group.set_index(['Month End Date']).resample('M').asfreq()

2. be notice that: 7/30/2020 is not the end day of July. 7/31/2020 is. so Using this method 7/30/2020 will be a problem(convert the Month End Date as the truely end date).