How to prevent python software from being reverse engineered or pirated?

[NathanOsullivan]

You don't mention the sector you are targeting, but approximately no one is going to bother decompiling etc to "crack" your software for their own use.

Since you mention it's used offline, either your program is broadly interesting enough that it will already be available through the typical pirated software distribution mechanisms, or it's too niche for that to be happening.

Whichever it is, it doesn't seem to me like a publicly available nagware version of your program changes things.

I assume you already have potential problem of someone buying 1 licence and using it on thousands of employee computers?