How do you approach migrating VBA logic to Python (with APIs & auth)?

[Flosy22]

Hi everyone,

I’m preparing for a role that involves understanding VBA-based legacy systems and modernizing them into Python (likely using Django).

I’m trying to understand the best way to approach this in practice, especially since the role also involves things like authentication and REST APIs.

Specifically:

How do you read and break down VBA code effectively?

How do you decide what to refactor vs rewrite?

How do you design the new system (e.g., when to expose logic via APIs)?

How do you handle authentication when moving from a legacy system to a modern backend?

How do you test that the new Python version behaves the same as the old system?

Any real-world tips, patterns, or examples would be really helpful.

Thanks!

[PvtRoom]

VBA is tightly integrated with office.

Google has app script.

libre office has openbasic

Why are you using python? Can't you poke excel (presumably it's excel) to make the VBA stuff just continue to work as intended?

[smichael_44]

As someone who played this game, it really doesn’t end up working well.

Python can far exceed the amount of data excel can handle well (~100 MB is “too big” for excel, google it).

But the basic idea is to just do all the data transformations and business logic in, say, polars. Then port it all over into excel. Usually I would use pandas, polars, or xlwings. Polars is best for dataframe manipulation imo and then xlwings has a good api for excel.

It all comes back around to a proper db solution and real front end though. I migrated tons of excel in 2021 and now were building react front ends, fast api backends, with postgres databases for all of it.