Python’s Hidden Superpower: Bytecode Hacking with dis and code Modules 🚀

Photo by Chris Ried on Unsplash

Most Python developers never explore how Python actually executes their code under the hood. But if you understand Python bytecode, you can:
✅ Optimize code at the lowest level
✅ Modify Python execution at runtime
✅ Write your own mini Python interpreter

Today, we’re diving into Python’s bytecode magic using the dis and code modules.

If you’ve never heard of bytecode hacking, prepare to be blown away. 🤯

🔹 1. What is Python Bytecode?

Before Python executes your code, it compiles it into an intermediate representation known as bytecode.

Bytecode is a low-level set of instructions that the Python interpreter executes.

📌 Example: Let’s see the bytecode for a simple function.

import dis

def add(x, y):
    return x + y

dis.dis(add)

✅ Output:

2           0 LOAD_FAST                0 (x)
              2 LOAD_FAST                1 (y)
              4 BINARY_ADD
              6 RETURN_VALUE

💡 What’s happening here?

• LOAD_FAST 0 (x) → Load x into the stack
• LOAD_FAST 1 (y) → Load y into the stack
• BINARY_ADD → Add them
• RETURN_VALUE → Return the result

This is exactly how Python executes your code!

🔹 2. How to Modify Python Bytecode? (Runtime Hacking) 🔥

📌 Changing Function Behavior Without Changing Source Code

Python stores the bytecode of a function in func.__code__. We can modify it on the fly!

def greet():
    return "Hello, World!"

print(greet())  # Normal output: Hello, World!

# Hack the bytecode: Change RETURN_VALUE to return "Hacked!"
greet.__code__ = (lambda: "Hacked!").__code__

print(greet())  # Now prints: Hacked!

✅ We just hacked a function’s behavior at runtime!

🔹 3. Manually Creating Python Functions…