I use "num-pee". It seems like the "correct" English pronunciation because of words like these: https://www.thefreedictionary.com/words-that-end-in-py
However, it does not surprise/bother me if someone goes for "num-pie".
However, it does not surprise/bother me if someone goes for "num-pie".
I mean the Py comes from python where it certainly sounds more like pie.
The real question then is: How would the file ending .py be pronounced?
When you have a consonant and a Y, it's generally quite common for that Y to make an "ai" sound. Like bylaw, dynamo, kyle, lying, rye, xylophone. So I'd say that Python's pronunciation is unexceptional.
In the case of pyramid, it comes from French pyramide so it follows the pronunciation of French. It's worth noting that both pyramid and pygmy have alternate/misspellings that use "pi" which shows that their spelling as "py" is not very natural to native speakers.