Calling Rust from Python/PyPy using CFFI (C Foreign Function Interface)

rust-python-cffi.md

This is a small demo of how to create a library in Rust and call it from Python (both CPython and PyPy) using the CFFI instead of ctypes.

Based on http://harkablog.com/calling-rust-from-c-and-python.html (dead) which used ctypes

CFFI is nice because:

• Reads C declarations (parses headers)
• Works in both CPython and PyPy (included with PyPy)
• Lower call overhead than ctypes

---

Install Rust

from either of:

• brew install rust
• Multirust

I recommend installing Rust via multirust so that you can compile projects that use unstable features (core) as well as testing for Rust 1.0,1.1, etc backwards compatibility.

The per-directory override mechanism is especially nice.

Build library

rustc treble.rs

This will create a libtreble.dylib

Run the Python client

python test.py 

<cffi.api.FFILibrary_./libtreble.dylib object at 0x1089d5490>
math from rust! 30

test.py

try:
    from cffi import FFI
except ImportError:
    print "pip install cffi, included with PyPy"

ffi = FFI()
lib = ffi.dlopen("./libtreble.dylib")

print lib
# <cffi.api.FFILibrary_./libtreble.dylib object at 0x107f440d0>

ffi.cdef('int treble(int);')

print "math from rust!", lib.treble(10)

treble.rs

#![crate_type = "dylib"]

#[no_mangle]
pub extern fn treble(value: i32) -> i32 {
    value * 3
}