Replacing ast.walk to make Python AST traversal 220x faster

Category: Engineering post
Status: confirmed
Sources: reflex.dev, fast-walk repository
Summary: The Reflex team traced slow Python AST traversal to the generator-based design of the standard library's ast.walk, which suspends and resumes execution on every node even when the caller consumes the full list. Walking difflib (about 7,000 nodes) took roughly 2ms, about 285 nanoseconds per node. Their replacement, released as the open-source fast-walk library, reports a 220x speedup by avoiding the generator overhead in the hot path.
Why it matters: Codegen and static-analysis tools that walk large ASTs repeatedly can cut latency substantially with a drop-in traversal change.