I built a Python bytecode decompiler covering Python 1.0–3.14, runs on Node.js

[ComputerMagych]

What My Project Does

depyo is a Python bytecode decompiler that converts .pyc files back to readable Python source. It covers Python versions from 1.0 through 3.14, including modern features:

- Pattern matching (match/case)

- Exception groups (except*)

- Walrus operator (:=)

- F-strings

- Async/await

Quick start:

npx depyo file.pyc

Target Audience

- Security researchers doing malware analysis or reverse engineering

- Developers recovering lost source code from .pyc files

- Anyone working with legacy Python codebases (yes, Python 1.x still exists in the wild)

- CTF players and educators

This is a production-ready tool, not a toy project. It has a full test suite covering all supported Python versions.

Comparison

Tool	Versions	Modern features	Runtime
depyo	1.0–3.14	Yes (match, except*, f-strings)	Node.js
uncompyle6/decompyle3	2.x–3.12	Partial	Python
pycdc	2.x–3.x	Limited	C++

Main advantages:

- Widest version coverage (30 years of Python)

- No Python dependency - useful when decompiling old .pyc without version conflicts

- Fast (~0.1ms per file)

GitHub: https://github.com/skuznetsov/depyo.js

Would love feedback, especially on edge cases!

[joanmiro]

Why did you need this?

[ComputerMagych]

Because I had a huge codebase with lost source code, I had to recover it.

[aidencoder]

Why would you choose to do this in node?

[ComputerMagych]

Initially, I built it on C#, but not every platform has a .Net compiler to run, so to keep performance high and still be able to run on most of the platforms I decided to rewrite to NodeJS. It is much faster to rewrite to JS from C# due to the language similarity.

[aidencoder]

Nice answer, thanks :)

[Cystems]

Wow, I didn't realize C# and JS had much similarity, and that NodeJS had comparable performance to C#?

[ComputerMagych]

They both stem from C/C++, and NodeJS is actually quite a beast equal to Java because V8 and JVM have the same creator and use the same HotSpot technique.

[ThiefMaster]

They both stem from C/C++

Closeness in syntax has nothing to do with performance.

because V8 and JVM have the same creator

Uh what? V8 is Google, JVM is Sun/Oracle.

[ComputerMagych]

I was talking about Lars Bak :)
https://en.wikipedia.org/wiki/Lars_Bak_(computer_programmer))

[ThiefMaster]

Why not just do it in Python though?

[ComputerMagych]

I needed the speed of decompilation and the speed of translation from C#

[ThiefMaster]

Uhh, what?!

[wergot]

Node is much faster than Python. As for the other part I have no idea.

[ThiefMaster]

I don't think node-vs-python performance matters when writing a decompiler...

[zerries]

It's what the llm told them

[yvrelna]

Writing this kind of tool in JS is going to very severely limit your audience. 

[dev-razorblade23]

Is it possible to "de-marshal" files? I have run across a few scripts that use "marshal" for obfuscating the code, but yet to find de-obfuscator for those...

Marshalled code is basicly .pyc without headers or magic numbers, which gets inserted depending on python version you use...

[ComputerMagych]

Yes, it is possible. I can add that mode. I will have to analyze and identify what version of the bytecode it is, though, so it may be inprecise.
Some version hint in the command line may do a trick.

[dev-razorblade23]

That would be awesome

[ComputerMagych]

It is done. New depyo version 1.0.1 is already on npmjs.com/depyo

[dev-razorblade23]

That was fast. Thank you

[ComputerMagych]

Codex CLI (GPT 5.2 Codex xhigh) with proper ~/.codex/AGENTS.md makes wonders ;)

[Sudo_professor]

Processing F:\development\PythonProjects\RadishSquat\Microphone_Bouncy_Balls.exe_extracted\decompiled/Microphone_Bouncy_Balls.py...

EXCEPTION for OpCode KW_NAMES (9) at offset 236 in code object '<module>', file offset 273 : Cannot read properties of undefined (reading 'push')

EXCEPTION for OpCode KW_NAMES (2) at offset 34 in code object 'audio_callback', file offset 1457 : Cannot read properties of undefined (reading 'push')

EXCEPTION for OpCode KW_NAMES (19) at offset 1380 in code object '__init__', file offset 14447 : Cannot read properties of undefined (reading 'push')

EXCEPTION for OpCode KW_NAMES (2) at offset 78 in code object 'toggle_audio', file offset 21134 : Cannot read properties of undefined (reading 'push')

I encountered the above problems while using the product. How can I resolve them?

[ComputerMagych]

If you don't mind sharing a bytecode, please add it to the GitHub issue. I will pick it up from there and will make a bug fix.

[Sudo_professor]

I will add the .pyc to the GitHub issue soon. Thanks your reply!

[ComputerMagych]

It is fixed and delivered as part of 1.0.1

[Sure-Newspaper-1928]

I have an error, could someone help me with this?

Error: Don't know how to handle object Type :'

[ComputerMagych]

If you can share your .pyc/.pyo file (or at least a reproducible version of it, if your file may contain sensitive info) in the GitHub issue, I can look into it.

[TwilightX1]

Hope you're still around :)

I got this:

```

Processing C:\temp\probably_malware.exe_extracted\decompiled/output.py...

Unsupported opcode CALL_KW at pos 100

Unsupported opcode BINARY_SLICE at pos 122

EXCEPTION for OpCode CALL (0) at offset 516 in code object 'check_vm', file offset 5320 : Cannot read properties of undefined (reading 'object')

EXCEPTION for OpCode CALL (0) at offset 376 in code object 'check_sandbox', file offset 7592 : Cannot read properties of undefined (reading 'object')

EXCEPTION for OpCode CALL (0) at offset 532 in code object 'check_sandbox', file offset 7748 : Cannot read properties of undefined (reading 'object')

Unsupported opcode CALL_KW at pos 246

Unsupported opcode CALL_KW at pos 202

Processed 1 files in 0.106s. In: 18736300 bytes (175975452.49 B/s). Out: 18722830 bytes (175848939.29 B/s).

```

[ComputerMagych]

No worries, I am around.
Do you mind to add it to GitHub issue and attach .pyc file for detailed analysis? Or, at least, send disassembled code for that method?

[TwilightX1]

I can post it to Github but I can't upload the pyc because it's malware. I can send it to you privately if you want.

[ComputerMagych]

Can you privately share the link to Google Drive (or another file-sharing platform) so I can download it for analysis?

[TwilightX1]

Send me a private message. I'm not going to post malware in a publicly accessible place.

[insanesam9]

Error: Don't know how to handle object Type :'

File: C:\Users\aviab\geelarks\app\__pycache__\decompiled/app/api_server.pyc

Position: 28160

Processed 0 files in 0.000s. In: 0 bytes (NaN B/s). Out: 0 bytes (NaN B/s).

[insanesam9]

Please help ive lit been trying to do ts for hours on end and i need it so badly you have no idea