cffi: واجهة الدوال الأجنبية لـ C

ما هي cffi؟

# pip install cffi
from cffi import FFI
ffi = FFI()

ffi.cdef("double sqrt(double x);")
libm = ffi.dlopen(None)   # current process
print(libm.sqrt(2.0))     # 1.4142...

وضع ABI مقابل وضع API

from cffi import FFI
ffi = FFI()

# ABI mode (no compile step):
ffi.cdef("int abs(int x);")
libc = ffi.dlopen("libc.so.6")  # Linux
print(libc.abs(-42))   # 42

تصريحات cdef

from cffi import FFI
ffi = FFI()

ffi.cdef("""
    typedef struct {
        double x;
        double y;
    } Point;

    double distance(Point a, Point b);
""")

# lib = ffi.dlopen("mylib.so")

إنشاء هياكل C

from cffi import FFI
ffi = FFI()

ffi.cdef("typedef struct { int x; int y; } Vec2;")
lib = ffi.dlopen(None)

v = ffi.new("Vec2 *")
v.x = 3
v.y = 4
print(v.x, v.y)   # 3 4

السلاسل والمخازن المؤقتة

from cffi import FFI
ffi = FFI()

buf = ffi.new("char[]", b"hello world")
print(ffi.string(buf))   # b"hello world"

# Mutable buffer for output:
out = ffi.new("char[128]")
# c_func(out, 128)  # fill the buffer
# result = ffi.string(out).decode()

وضع API مع verify

from cffi import FFI
ffi = FFI()

ffi.cdef("int add(int a, int b);")
ffi.set_source("_mylib",
    """
    int add(int a, int b) { return a + b; }
    """
)

# Build: python build_mylib.py
# from _mylib import ffi, lib
# print(lib.add(3, 4))   # 7

الاستدعاءات الراجعة من C إلى Python

from cffi import FFI
ffi = FFI()
ffi.cdef("typedef int (*compare_fn)(int, int);")

@ffi.callback("int(int, int)")
def compare(a, b):
    return a - b

# pass compare to a C sort function

إدارة الذاكرة

from cffi import FFI
ffi = FFI()

# ptr freed when Python GC collects it:
buf = ffi.new("int[10]")
buf[0] = 42
print(buf[0])   # 42

# Custom destructor:
# ptr = ffi.gc(lib.alloc(), lib.free)

cffi مقابل ctypes

# ctypes approach:
import ctypes
libc = ctypes.CDLL("libc.so.6")
libc.abs.restype = ctypes.c_int
libc.abs.argtypes = [ctypes.c_int]
print(libc.abs(-5))   # 5

# cffi approach:
from cffi import FFI; ffi = FFI()
ffi.cdef("int abs(int);")
lib = ffi.dlopen(None)
print(lib.abs(-5))    # 5

استخدام cffi مع NumPy

import numpy as np
from cffi import FFI
ffi = FFI()

arr = np.array([1.0, 2.0, 3.0])
ptr = ffi.cast("double *", arr.ctypes.data)
# Now ptr can be passed to a C function expecting double*

معالجة الأخطاء باستخدام cffi

import errno as errno_mod
from cffi import FFI
ffi = FFI()
ffi.cdef("int open(const char *path, int flags);")
lib = ffi.dlopen(None)

fd = lib.open(b"/nonexistent", 0)
if fd == -1:
    err = ffi.errno
    raise OSError(err, "open failed")

تحقق سريع

مراجعة