Thanks for the excellent question! It’s true that there is not a Python interpreter in iOS out of the gate, as you said. Getting Python to run on iOS is an interesting challenge by itself.
There are solutions out there for running Python on iOS. However, that doesn’t get us all the way. Although I could be wrong, I don’t believe Swift 4.2 interacting with Python on an iOS device is yet in existence.
dynamicMemberLookup offers great support for interoperability between Swift and Python, other pieces have to fall into place to make it all happen on iOS. One of them is a strong interest in the effort.
For example, interest in Swift / Python interoperability has been driven by Chris Lattner due to the energy around TensorFlow, an open-source software library used for machine learning.
However, that doesn’t get us what we want on an iOS device yet either. The emphasis there is on the server side as opposed to the client iOS devices.
Digging into StackOverflow reveals that at least one person had installed a Pythonista template on their iPhone and it satisfied their Swift / Python needs. Given other scraps of information I could glean from the Internet, I don’t believe Pythonista currently supports Swift 4.2.
So, we’re not quite there yet when it comes to Swift and Python working together on iOS. Until then server side Swift / Python interoperability will continue to grow. At least an iOS device can reach out to the server for whatever information it needs. That might fulfill whatever needs one has.
I hope this answers your question. Thank you for asking it. :]