ctypes.CDLL
- Python course
- Expert
- Lesson 19/47
- 5 min
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.
Practice 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.
Starter code
# load libc
# call the abs function
# print the resultSample solution
import ctypes
libc = ctypes.CDLL(None)
result = libc.abs(-7)
print(result)Expected output
7
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 Match CDLL concepts
| Term | Meaning |
|---|---|
CDLL |
Loads a library |
None |
Default libc |
.abs(-7) |
Function call |
c_int |
Default return |
2 What does CDLL(None) load?
import ctypes
libc = ctypes.CDLL(None)- The default C library Correct answer
- A Python standard module
- It raises an error
- An empty object
Explanation: CDLL(None) loads the default C library of the process.
3 Complete the CDLL call
libc = ctypes.____(None)libc = ctypes.CDLL(None)Explanation: CDLL(None) loads the default C library.