Not for the time being - to allow us to run code on the edge, and be able to support many customers, we used V8 (a JavaScript engine) since it built for multi-tenant-per-process secure sandboxing, fast start time, and low overhead (a lot of this is explained in the original blog post here: https://blog.cloudflare.com/introducing-cloudflare-workers/).
We are working on improving our WebAssembly integration, and making it a first-class experience (and we launched multiple improvements with the CLI to allow you to more seamlessly develop in Rust, C and C++). Maybe one day Python WebAssembly will take off.