the data is serialized as JSON or YAML. When we are less fortunate, we get an Excel spreadsheet or a CSV file which is always broken in some way, can't explain it.
I don't have any data to support this next claim, but I'm fairly sure that Excel is the most common way to store, manipulate, and yes(!), even pass data around. This is why it's not uncommon to find yourself reading Excel in Python. I recently needed to, so I tested and bench...