Integrating Python with C for Performance — Using ctypes

This guide demonstrates how to write C functions, compile them into a shared library, and use them inside Python using the ctypes module. This allows Python to leverage the speed of compiled C code, especially useful in performance-heavy computations.

What You Will Learn

How to write reusable C functions.

How to compile C code into a shared library (.dll / .so).

How to load and call C functions using Python's ctypes.

How data is passed between Python and C.

🧾 Step 1: Write the C Code

Create a file named Functions.c:

int lcm(int a,int b){ int l; for(l = a > b ? a : b; l <= a*b; l++){ if(l % a == 0 && l % b == 0){ return l; } } }

int fact(int n){ int f = 1; for(int i=1; i<=n; i++){ f = f * i; } return f; }

This file contains two functions:

lcm(a, b) → Calculates Least Common Multiple.

fact(n) → Calculates factorial of a number.

🛠️ Step 2: Compile the C Code into a Shared Library For Linux / Mac: gcc -std=c11 -o customlib1.so --shared -fPIC Functions.c

For Windows (MinGW): gcc -shared -o customlib1.dll Functions.c

After compiling, you will get:

customlib1.so (Linux/Mac) or

customlib1.dll (Windows)

🐍 Step 3: Use the Library in Python

Create main.py:

from ctypes import *

Load the shared library (update the path as needed)

c_file_path = r"D:\100 days\31th\customlib1.dll" c_fun = CDLL(c_file_path)

Call C functions

a = c_fun.lcm(4, 6) b = c_fun.fact(5)

print("The LCM is:", a) print("The Factorial is:", b)

⚡ Output The LCM is: 12 The Factorial is: 120

🧠 Why Use C with Python? Feature Python C Ease of writing ✅ Easy ⚠️ Complex Execution Speed ⏳ Slower ⚡ Very fast Use Case High-level logic, scripting Heavy computation, algorithms

Using both together gives the best of both worlds.

Conclusion

By integrating Python and C, you gain fast execution without losing Python’s simplicity. This approach is widely used in AI, Game Engines, Data Processing, and System Tools.