Exploring CPython's bytecode

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" summary

Walks the .pyc layout (magic number, timestamp, code object) and uses the standard library marshal and imp to read Python 3.2 bytecode, dis to inspect opcodes, then implements a tiny Python VM in Python that creates frame objects, an instruction pointer and a stack and executes LOAD_FAST/STORE_FAST, MAKE_FUNCTION, CALL_FUNCTION and arithmetic ops successfully. It skips defaults, keyword and keyword-only args, is intentionally slow but functional, and notes a hidden limit: bytecode argument encoding caps positional args at 255 arguments. VM loop and frame object implemented in pure Python.

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" chapters (38)

1. 0:00Intro
2. 1:26Unravelling Bytecode
3. 2:32Python: Compiler & VM
4. 3:45Python overview
5. 4:21Example Module
6. 5:07Executing the Bytecode
7. 7:33Optimisation
8. 8:55Structure of .pyc Files
9. 10:07Magic Number
10. 11:53Timestamp
11. 12:16Code Object Marshal module
12. 14:08Back to the Compiler Compile your own code object
13. 16:28Code Objects It's documented: Data model (Language Reference) Everything which is executed becomes a code
14. 19:21sum Code Object
15. 20:59Disassembler
16. 24:10First Taste of Bytecode (2) LOAD FAST
17. 24:36First Model of the VM
18. 26:04Reading Bytecode
19. 27:07Bytecode Arguments dis HAVE ARGUMENT = 90
20. 27:38First Eval Loop
21. 29:25Passing Arguments
22. 31:15Handling Bytecodes
23. 31:32LOAD FAST LOAD CONST
24. 31:57BINARY MULTIPLY
25. 33:37BINARY ADD
26. 34:01RETURN VALUE
27. 34:24The VM So Far
28. 34:48Disassembling the Module
29. 38:22STORE NAME LOAD NAME
30. 43:35CALL FUNCTION (2)
31. 44:05POP JUMP_IF_FALSE
32. 44:31JUMP FORWARD . POP TOP
33. 45:14Incomplete
34. 45:29EXTENDED ARG
35. 46:00Abusing Bytecode
36. 46:10The Tools
37. 46:20Improve Tracing
38. 46:58Questions

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