How to call a C library function from Python using ctypes?

Table of Contants

Introduction

In Python, the ctypes library allows you to call functions from C libraries (like .dll, .so, or .dylib) directly. This can be useful for accessing optimized C code or utilizing existing C libraries in Python applications. By defining function prototypes, you can interact with these libraries just like you would in C.

Steps to Call a C Library Function Using ctypes

1. Loading the Shared Library

First, load the shared C library using ctypes.CDLL (for Linux/macOS .so libraries) or ctypes.WinDLL (for Windows .dll libraries). Here's how:

2. Defining the C Function Prototype

Define the argument types and return type of the C function using the argtypes and restype attributes.

Argument Types

Define the types of arguments the C function expects using argtypes.

Return Type

Define the return type of the function using restype.

3. Calling the C Function

Now, you can call the C function from Python just like any Python function, passing arguments that match the function's expected types.

Practical Examples

Example 1: Calling a Simple C Function

Assume you have the following C function in a shared library:

To call this function from Python:

Example 2: Function with Pointers

If the C function expects pointers, use ctypes.byref() or ctypes.POINTER().

Python code:

Example 3: Function with Strings

When passing strings, use ctypes.c_char_p for C-style strings.

Python code:

Conclusion

Using ctypes, you can easily call C library functions from Python by loading the shared library, defining the function prototypes, and calling the functions with appropriate arguments. This allows you to take advantage of high-performance C code within Python applications for better efficiency.