The fingerprint is always in the signature (when the signature packets are well-formed). The public key is almost always not. I think it would behoove you to read the post linked in TFA, which explains this in detail[1].
In general in Software you have to start with an idea of what you want to accomplish. Then you have to break that down and determine what is feasible within the constraints you are working. Ideally you then point out the constraints that are limiting your solution. I feel like all of that is missing here. All I can see there is just an immense sea of details.
[1]: https://blog.yossarian.net/2023/05/21/PGP-signatures-on-PyPI...