cffi

Learn to call C code with cffi.

What is cffi?

cffi (C Foreign Function Interface) is an alternative to ctypes. It lets you write C header declarations directly in Python.

You create an FFI object, declare C signatures with ffi.cdef, then load the library with ffi.dlopen. Two advantages over ctypes: signatures are written in C syntax (more natural) and type checking happens at parse time. cffi is also faster than ctypes on PyPy.

C code with cffi

Using cffi takes three steps: create FFI(), declare the signature with ffi.cdef('int abs(int);'), load the library with lib = ffi.dlopen(None).

You then call the function with lib.abs(-9). Since the signature is in C syntax it is easy to copy from header files. Errors in cdef are caught at parse time; there are no runtime crashes like with ctypes. This makes cffi safer for large C APIs.

Exercise Call strlen with cffi

Import with from cffi import FFI. Create an FFI() object. Declare the signature with ffi.cdef('size_t strlen(const char*);'). Load the library with ffi.dlopen(None). Print the result of lib.strlen(b"dunya").

Show example solution

from cffi import FFI

ffi = FFI()
ffi.cdef("size_t strlen(const char*);")
lib = ffi.dlopen(None)
print(lib.strlen(b"dunya"))

Test yourself

Match cffi concepts

FFI

Interface object
cdef

C declaration
dlopen

Loads a library
cffi

ctypes alternative
What does cffi provide?
```
from cffi import FFI
ffi = FFI()
ffi.cdef('int abs(int);')
```
- Running SQL from Python
- Writing C declarations in Python
- Generating web pages
- File compression
Show answer

Writing C declarations in Python — answer: writing C declarations in Python. cffi is designed for C interfaces.

Complete the cffi call

ffi = FFI()
ffi.____('int abs(int);')

Show answer

ffi = FFI()
ffi.cdef('int abs(int);')

Next lesson: Structure

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