If you want to upload very large files into an Anvil app, you might experience timeouts or exceed your Data Tables storage. Instead, it makes sense to store large files in a cloud storage service, such as Amazon S3.
Meredydd and I have written a guide on how to upload large files directly to S3 from an Anvil app! It uses Amazon’s boto3 library and the uppy.io JS widget (using Python).
Since it accepts a file handler, I don’t see why you couldn’t shove it into a file stream and operate it in memory without even writing it to disk.
(Lets say you are going to immediately load it into a pandas dataframe or something, why write to disk)