Understanding Python 3.13 Copy‑and‑Patch JIT Compiler

Python 3.13 introduces a copy-and-patch JIT compiler, a significant change in the language’s history aimed at increasing the execution speed of Python code.

The JIT compiler represents a major step in Python performance optimization, especially for high‑performance computing scenarios.

When Python code runs for the first time, the JIT compiler translates it into machine language and reuses the compiled code in subsequent executions, meaning the program becomes faster as more code is compiled.

This approach differs from traditional interpretation, where each execution requires re‑interpretation; the JIT compiler incurs compilation cost only on the first run.

The new JIT uses a Copy-and-patch design that converts bytecode into a set of "templates" and patches them with the correct values at runtime.

It relies heavily on the LLVM ecosystem, employing tools such as Clang with -O3 optimization, llvm-objdump , and llvm-readelf to produce efficient machine code.

The advantage of the Copy-and-Patch technique is that developers do not need to write assembly code manually; the generated machine code is both high‑performance and quickly produced at runtime.

Ordinary Python users will not need to manage complex JIT compiler architectures in their runtime.

Finally, the author notes that once Python 3.13 is officially released, a comparative test between the old and new compilers will be performed.