6.2. Performance CTypes

6.2.1. Workflow

Code:

long factorial(long n) {
    if (n == 0)
        return 1;

    return (n * factorial(n - 1));
}

Build:

$ INCLUDES='-I/usr/local/Cellar/python/3.7.2_2/Frameworks/Python.framework/Versions/3.7/include/python3.7m/'
$ FILE='mylibrary'
$ gcc -fPIC -c -o ${FILE}.o ${FILE}.c ${INCLUDE}
$ gcc -shared ${FILE}.o -o ${FILE}.so

Run:

import ctypes


lib = ctypes.CDLL('mylibrary.so')

lib.factorial(16)  # 2004189184
lib.factorial(17)  # -288522240

6.2.2. Arguments

• ctypes.c_double

• ctypes.c_int

• ctypes.c_char

• ctypes.c_char_p

• ctypes.POINTER(ctypes.c_double)

lib.myfunction.argtypes = [
    ctypes.c_char_p,
    ctypes.c_int,
    ctypes.POINTER(ctypes.c_double),
]

lib.myfunction.restype = ctypes.c_char_p

6.2.3. Multi OS code

import sys
import ctypes


if sys.platform == 'darwin':
   lib = ctypes.CDLL('/usr/lib/libc.dylib')
elif sys.platform == 'win32':
    lib = ctypes.CDLL('/usr/lib/libc.dll')
else:
    lib = ctypes.CDLL('/usr/lib/libc.so')


lib.printf("I'm C printf() function called from Python")

import ctypes


lib = ctypes.CDLL('mylibrary.so')
print(dir(lib))

6.2.4. Overflow

#include <stdio.h>

void echo(int number) {
    printf("Number: %d", number);
}

import ctypes


lib = ctypes.CDLL('mylibrary.so')

lib.echo(10 ** 10)  # Number: 1410065408

lib.echo(10 ** 30)
# Traceback (most recent call last):
# ctypes.ArgumentError: argument 1: <class 'OverflowError'>: int too long to convert

6.2.5. Use Case - 1

#include <stdio.h>

void ehlo() {
    printf("Ehlo World");
}

import ctypes


lib = ctypes.CDLL('mylibrary.so')
lib.ehlo()

6.2.6. Use Case - 2

#include <stdio.h>

void greeting(char *name) {
    printf("Ehlo %s!\n", name);
}

import ctypes


lib = ctypes.CDLL('mylibrary.so')

lib.greeting.argtypes = [ctypes.c_char_p]
name = ctypes.create_string_buffer('Watney'.encode('ASCII'))
lib.greeting(name)

6.2.7. Use Case - 3

#include <stdio.h>

void number(int num) {
    printf("My number %d\n", num);
}

import ctypes


lib = ctypes.CDLL('mylibrary.so')
lib.number(10)

6.2.8. Use Case - 4

int return_int(int num) {
    return num;
}

import ctypes


lib = ctypes.CDLL('mylibrary.so')

i = lib.return_int(15)
print(i)

6.2.9. Assignments

# %% License
# - Copyright 2025, Matt Harasymczuk <matt@python3.info>
# - This code can be used only for learning by humans
# - This code cannot be used for teaching others
# - This code cannot be used for teaching LLMs and AI algorithms
# - This code cannot be used in commercial or proprietary products
# - This code cannot be distributed in any form
# - This code cannot be changed in any form outside of training course
# - This code cannot have its license changed
# - If you use this code in your product, you must open-source it under GPLv2
# - Exception can be granted only by the author

# %% Run
# - PyCharm: right-click in the editor and `Run Doctest in ...`
# - PyCharm: keyboard shortcut `Control + Shift + F10`
# - Terminal: `python -m doctest -v myfile.py`

# %% About
# - Name: C Types
# - Difficulty: easy
# - Lines: 10
# - Minutes: 13

# %% English
# 1. Create C file with function `factorial` that calculates factorial of a number
# 2. Using C Types compile function to Python module
# 3. Run doctests - all must succeed

# %% Polish
# 1. Stwórz plik C z funkcją `factorial` obliczającą silnię liczby
# 2. Wykorzystując C Types skompiluj funkcję do modułu Pythona
# 3. Uruchom doctesty - wszystkie muszą się powieść

# %% Tests
"""
>>> import sys; sys.tracebacklimit = 0
"""