The Forbidden Python: Using ctypes to Break All the Rules

Python is known for its simplicity, readability, and safety. But what if I told you there’s a way to bypass Python’s safeguards, manipulate memory directly, and even crash the interpreter—all with a built-in library?

Enter ctypes—Python’s secret backdoor into the world of low-level programming.

1. What is ctypes?

ctypes is a foreign function interface (FFI) that allows Python to call C functions and interact with raw memory, shared libraries (*.so, *.dll), and system APIs. With great power comes great responsibility—and the ability to break Python’s rules in ways you never thought possible.

2. Breaking Python’s Safety Guards

Modifying Immutable Objects (Yes, Really)

Python’s str and tuple types are supposed to be immutable. But with ctypes, we can forcefully change them:

import ctypes  

def hack_string():  
    s = "hello"  
    # Get memory address of the string  
    addr = id(s)  
    # Overwrite memory using ctypes  
    ctypes.memmove(addr + 20, b"world", 5)  
    print(s)  # Might print "world" (UNDEFINED BEHAVIOR!)  

hack_string()  

⚠️ Warning: This is unsafe, unpredictable, and can crash Python. But it proves that immutability is just a convention—not a hard rule.

Executing Arbitrary Memory

Want to run machine code directly from Python? ctypes lets you:

import ctypes  

# Shellcode (Linux x64 "/bin/sh" example)  
shellcode = b"\x48\x31\xff\x48\x31\xf6\x48\x31\xd2\x48\x31\xc0\x50\x48\xbb\x2f\x62\x69\x6e\x2f\x2f\x73\x68\x53\x48\x89\xe7\xb0\x3b\x0f\x05"  

# Allocate executable memory  
buf = ctypes.create_string_buffer(shellcode)  
addr = ctypes.addressof(buf)  

# Cast to a function and execute  
func = ctypes.CFUNCTYPE(None)(addr)  
func()  # Runs /bin/sh (if you dare!)  

🚨 Danger: This is how malware works. Never run untrusted shellcode!

3. Bypassing Python’s GIL

The Global Interpreter Lock (GIL) prevents true multithreading in Python—but ctypes lets you call C functions that ignore it:

from ctypes import CDLL, c_int  
import threading  

libc = CDLL("libc.so.6")  # Linux  

def cpu_bound_task():  
    libc.sleep(1)  # Bypasses GIL since it’s a C call  

# Real parallel execution (unlike threading.Thread)  
threads = [threading.Thread(target=cpu_bound_task) for _ in range(10)]  
[t.start() for t in threads]  
[t.join() for t in threads]  

This won’t speed up pure Python code, but it shows how ctypes can escape Python’s limitations.

4. Hacking Python Internals

You can even modify Python’s runtime behavior by tweaking internal C structures:

import ctypes  

# Disable Python's GC (DANGEROUS!)  
def disable_gc():  
    import gc  
    gc.disable()  
    # Forcefully re-enable it via C (because why not?)  
    libc = ctypes.CDLL("libc.so.6")  
    libc.free(ctypes.c_void_p(id(gc) + 0x20))  # Pure evil  

disable_gc()  

🔥 This can corrupt memory and crash your program. Use at your own risk.

5. Why Would Anyone Do This?

• Reverse engineering (modifying running processes)
• High-performance C extensions (without writing C)
• Security research (exploiting memory vulnerabilities)
• Just because you can (and to understand Python deeper)

Conclusion: Should You Use ctypes Like This?

No… unless you really know what you’re doing.

ctypes is a powerful tool, but most projects should stick to safer alternatives like:

• CFFI (a more stable FFI)
• Rust + PyO3 (for safe, fast extensions)
• Plain C extensions (for production code)

But if you’ve ever wanted to break Python’s rules, now you know how.

Have you ever used ctypes for something crazy? Share your stories below! 👇