Disassembling CPython Opcodes with dis Module

1Concept

CPython uses a virtual stack machine. Bytecode opcodes manipulate values on the frame's evaluation stack. Opcodes like `LOAD_FAST`, `STORE_FAST`, `BINARY_OP`, and `RETURN_VALUE` execute inside the main C loop.

2Architecture Diagram

CPython Evaluation Stack:
 [ LOAD_FAST salary ] ---> [ LOAD_FAST rate ] ---> [ BINARY_OP (Mult) ] ---> [ RETURN_VALUE ]
      |salary|                  |rate|                     |res|                 |res|
      +------+                  |salary|                   +---+                 +---+
                                +------+

3Code Example

import dis

def multiply(a: int, b: int) -> int:
    return a * b

print("=== Bytecode Disassembly for multiply() ===")
dis.dis(multiply)

4Expected Output

=== Bytecode Disassembly for multiply() ===
  5           0 RESUME                   0
  6           2 LOAD_FAST                0 (a)
              4 LOAD_FAST                1 (b)
              6 BINARY_OP                5 (*)
             10 RETURN_VALUE

5Key Takeaways

• ✓LOAD_FAST reads local variables directly from frame array without dict lookup.
• ✓Python 3.11+ replaced BINARY_MULTIPLY with generalized BINARY_OP opcode.
• ✓RETURN_VALUE pops top of stack and returns control to caller frame.