How do I protect Python code from being read by users?

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I am developing a piece of software in Python that will be distributed to my employer’s customers. My employer wants to limit the usage of the software with a time-restricted license file.

If we distribute the .py files or even .pyc files it will be easy to (decompile and) remove the code that checks the license file.

Another aspect is that my employer does not want the code to be read by our customers, fearing that the code may be stolen or at least the “novel ideas”.

Is there a good way to handle this problem?

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“Is there a good way to handle this problem?” No. Nothing can be protected against reverse engineering. Even the firmware on DVD machines has been reverse engineered and the AACS Encryption key exposed. And that’s in spite of the DMCA making that a criminal offense.

Since no technical method can stop your customers from reading your code, you have to apply ordinary commercial methods.

  1. Licenses. Contracts. Terms and Conditions. This still works even when people can read the code. Note that some of your Python-based components may require that you pay fees before you sell software using those components. Also, some open-source licenses prohibit you from concealing the source or origins of that component.

  2. Offer significant value. If your stuff is so good — at a price that is hard to refuse — there’s no incentive to waste time and money reverse engineering anything. Reverse engineering is expensive. Make your product slightly less expensive.

  3. Offer upgrades and enhancements that make any reverse engineering a bad idea. When the next release breaks their reverse engineering, there’s no point. This can be carried to absurd extremes, but you should offer new features that make the next release more valuable than reverse engineering.

  4. Offer customization at rates so attractive that they’d rather pay you to build and support the enhancements.

  5. Use a license key which expires. This is cruel, and will give you a bad reputation, but it certainly makes your software stop working.

  6. Offer it as a web service. SaaS involves no downloads to customers.

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