ctypes.CDLL

Learn to load native libraries with ctypes.CDLL.

What is ctypes.CDLL?

The ctypes module lets Python call native C libraries. The CDLL class loads a shared library and exposes its functions.

CDLL(None) loads the default C library (libc on Linux). You can then call functions like libc.abs(-7) through the loaded object. The default return type is c_int. This is the most direct way to bridge Python and C, and is common in systems programming.

Calling a function

You access functions on a CDLL object with a dot: libc.abs(-7). Python converts arguments to C types automatically.

The default return type is c_int. If the function returns a different type (such as size_t) you must specify it with restype. Otherwise the return value may be truncated. The call is synchronous and fast as in C; but type mismatches can cause crashes.

Exercise Call abs with CDLL

Import the module with import ctypes. Load the default C library with ctypes.CDLL(None). Assign the result of libc.abs(-7) to a variable and print it.

Show example solution

import ctypes

libc = ctypes.CDLL(None)
result = libc.abs(-7)
print(result)

Test yourself

Match CDLL concepts

CDLL

Loads a library
None

Default libc
.abs(-7)

Function call
c_int

Default return
What does CDLL(None) load?
```
import ctypes
libc = ctypes.CDLL(None)
```
- The default C library
- A Python standard module
- It raises an error
- An empty object
Show answer

The default C library — CDLL(None) loads the default C library of the process.

Complete the CDLL call

libc = ctypes.____(None)

Show answer

libc = ctypes.CDLL(None)

Next lesson: ctypes types

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