Summary - ctypes and CFFI

Combine CDLL, types and Structure to write a native wrapper.

Recap: ctypes and cffi

In this group you learned to call native C code from Python. You loaded libraries with CDLL and used C types with c_int and c_char_p.

You declared signatures with argtypes and restype. You saw the C-syntax alternative cffi. You modeled C structs with Structure. Now you will combine these into a native wrapper: a Point struct and an abs call together.

Exercise Write a native wrapper

Import the module with import ctypes. Write a Point(ctypes.Structure) class; define _fields_ = [('x', ctypes.c_int), ('y', ctypes.c_int)]. Load the library with libc = ctypes.CDLL(None). Create an instance with Point(-3, 4). Print the result of libc.abs(p.x).

Show example solution

import ctypes

class Point(ctypes.Structure):
    _fields_ = [("x", ctypes.c_int), ("y", ctypes.c_int)]

libc = ctypes.CDLL(None)
p = Point(-3, 4)
print(libc.abs(p.x))

What you learned

In this group you learned to bridge Python and native C code. You loaded libraries with CDLL and used C types and signature declarations.

You saw the C-syntax alternative cffi. You modeled C structs with Structure. In the summary you combined a struct and a function call. This knowledge is important for systems programming and performance-critical applications.

Test yourself

Match all ctypes concepts

CDLL

Loads a library
c_int

C int type
argtypes

Argument types
Structure

C struct
Which tool for which job?
- CDLL to define a struct
- argtypes to declare a signature
- Structure to load a library
- cffi to make a web page
Show answer

argtypes to declare a signature — answer: argtypes to declare a signature. CDLL loads a library, Structure defines a struct.

Final blank

libc = ctypes.____(None)

Show answer

libc = ctypes.CDLL(None)

Next lesson: Process

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