[mshockwave]

It's likely that Swift compiler is using LLVM LIT (https://llvm.org/docs/CommandGuide/lit.html), which is implemented in python, as the test driver

[airspeedswift]

Python and LIT are used heavily to build and test the compiler, but that is only for building it, you do not need it to download and use the built toolchain. The python dependency is more about its use in LLDB.