I know that a python exe file easily can get decompiled and the license code easily can get bypassed too. However my target group is not smart enou...
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you could give them a "key" that is a hash of their user ID and the time of registration or something identifiable like that. then, when they open your program, ping your server in the background, verifying that the key is valid and belongs to the database as well as the user stored on the local machine.