Serc: CPython bytecode compiler written in Rust (Codex built, 2-4x speedup)

Astral Experiments released Serc, an experimental CPython bytecode compiler written in Rust, which produces byte-for-byte identical output to CPython on Django, Airflow, and Transformers across CPython 3.12, 3.13, 3.14, and 3.15 at optimization levels 0, 1, and 2, while compiling 3-4x faster than CPython's compileall. The project's README states that all code changes, PR summaries, and additional documentation were authored entirely by GPT in Codex, and warns that Serc is experimental and may emit incorrect bytecode in some cases. Serc installs from crates.io as serc-cli with Rust 1.96 or later, emits Python 3.14-compatible bytecode by default, and supports --python-version targeting for 3.12 through 3.15.

An experimental CPython bytecode compiler, written in Rust. Serc produces byte-for-byte identical output as compared to CPython on an extensive corpus of real-world Python code, including Django https://github.com/django/django , Airflow https://github.com/apache/airflow , and Transformers https://github.com/huggingface/transformers , across CPython 3.12, 3.13, 3.14, and 3.15, and optimization levels 0, 1, and 2, all while compiling 3-4x faster https://github.com/astral-experiments/serc/blob/main/BENCHMARKS.md project-compilation than CPython’s compileall . But Serc is also experimental And so may emit incorrect bytecode in some cases. Warning Serc is experimental. This README is human-edited, but all code changes, PR summaries, and additional documentation were authored entirely by GPT in Codex. Install from crates.io https://crates.io/crates/serc-cli with Rust 1.96 or later: cargo install serc-cli --locked Given hello.py : python def greet name : return f"Hello, {name} " Compile to bytecode, emitted at pycache /hello.cpython-314.pyc : serc compile hello.py Pass a directory to compile its Python files recursively, or use --check to compile without writing cache files: serc compile path/to/package serc compile --check path/to/package Compilation uses the available CPUs by default. Use --jobs or -j on the command line or the RAYON NUM THREADS environment variable to set a limit, including --jobs 1 for serial compilation. serc compile --jobs 4 path/to/package By default, Serc skips files whose .pyc is up to date by checking the bytecode format and invalidation mode, then comparing the source file's timestamp and size for timestamp-based caches or its content hash for hash-based caches . Pass --force or -f to recompile every file, for example after switching compilers or native build profiles. Even with --force , Serc refuses to overwrite symlinks or special files. Serc emits Python 3.14-compatible bytecode by default, but supports target selection with --python-version . For example, to emit Python 3.15 bytecode: serc compile --python-version 3.15 path/to/package Serc supports the following CPython minor versions: | Target | Pinned CPython release | |---|---| | 3.12 | 3.12.14 | | 3.13 | 3.13.15 | | 3.14 | 3.14.5 | | 3.15 | 3.15.0rc2 | Each target writes its own cache tag and bytecode magic number, so the four versions can coexist under pycache . Use -O to remove assertions and set debug to false, matching Python's -O mode. Use -OO to additionally remove module, class, and function docstrings: serc compile -O hello.py serc compile -OO hello.py You can also select the level explicitly with --optimize 0 , --optimize 1 , or --optimize 2 . Level 0 is the default. Optimized caches use Python's naming convention, such as pycache /hello.cpython-314.opt-1.pyc and pycache /hello.cpython-314.opt-2.pyc , so all three levels can coexist. Add Serc to your Cargo.toml : dependencies serc = "0.1.0" Compile Python source and serialize the resulting code object in CPython's marshal format: js let module = serc::compile "print 'Hello, world ' \n", "hello.py" .unwrap ; let marshaled = module.marshal ; Serc is licensed under either of - Apache License, Version 2.0, LICENSE-APACHE https://github.com/astral-experiments/serc/blob/main/LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0 https://www.apache.org/licenses/LICENSE-2.0 - MIT license LICENSE-MIT https://github.com/astral-experiments/serc/blob/main/LICENSE-MIT or https://opensource.org/licenses/MIT https://opensource.org/licenses/MIT at your option. Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in Serc by you, as defined in the Apache-2.0 license, shall be dually licensed as above, without any additional terms or conditions.