# Python Ctypes Module

The `ctypes` module is a foreign function library for Python. It provides C compatible data types, and allows calling functions in DLLs or shared libraries. It can be used to wrap these libraries in pure Python.

## Importing the Module

```python
import ctypes
```

## Loading Shared Libraries

You can load shared libraries (DLLs on Windows, .so files on Linux) using `ctypes.CDLL` or `ctypes.WinDLL`.

```python
import ctypes
import os

# Load the C standard library (example for Windows)
if os.name == 'nt':
    libc = ctypes.CDLL("msvcrt.dll")
else:
    # Example for Linux
    libc = ctypes.CDLL("libc.so.6")
```

## Calling Functions

Once loaded, you can call functions from the library like normal Python functions. Note that C functions often require bytes strings instead of Python strings.

```python
libc.printf(b"Hello, %s\n", b"World")
```

## Data Types

`ctypes` provides a number of primitive C compatible data types.

*   `ctypes.c_int`: Represents a C signed int.
*   `ctypes.c_float`: Represents a C float.
*   `ctypes.c_char_p`: Represents a C char * (string).
*   `ctypes.c_void_p`: Represents a C void *.

```python
i = ctypes.c_int(42)
print(i.value) # Output: 42
```

## Structures

You can define C structures and unions by subclassing `ctypes.Structure` and `ctypes.Union`.

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

point = Point(10, 20)
print(f"Point: ({point.x}, {point.y})")
```

[[programming/python/python]]