JustJIT Documentation

JustJIT is a Python JIT compiler that uses LLVM ORC to compile Python bytecode directly to native machine code.

import justjit

@justjit.jit(mode='int')
def sum_loop(n):
    total = 0
    for i in range(n):
        total = total + i
    return total

# 38,000x faster than CPython
sum_loop(10_000_000)

Features

  • Compiles Python bytecode to LLVM IR, then to native machine code

  • 12 native compilation modes for maximum performance (int, float, bool, complex, SIMD, etc.)

  • Inline C/C++ compilation - embed and call C code directly from Python

  • Generator and async function support via state machine compilation

  • No interpreter overhead for numeric loops

  • Near-complete Python 3.13 opcode coverage (75+ opcodes)

  • Simple decorator-based API

  • Cross-platform support (Windows x64, macOS arm64, Linux x64)

Quick Start

Install from PyPI:

pip install justjit

Use the @jit decorator:

import justjit

@justjit.jit(mode='float')
def add(a, b):
    return a + b

result = add(3.0, 4.0)  # Runs as native code

User Guide

Reference

Advanced

Indices and tables