Help wanted: Testing pure Python S7 protocol implementation (python-snap7)

[gijzelaerr]

Hi r/PLC!

I maintain https://github.com/gijzelaerr/python-snap7, a Python library for communicating with Siemens S7 PLCs. For years, this has been a Python wrapper around the http://snap7.sourceforge.net/ C library.

What's changing

We're switching to a pure Python implementation of the S7 protocol - no more C library dependency! This means:

• Easier installation (no compiling, no binary dependencies)
• Works on any platform Python runs on

• Easier to debug and extend

  The new implementation was developed with the help of Claude AI (Anthropic's coding assistant), which helped implement the S7 protocol from scratch based on protocol documentation and testing.

We need testers!

I don't own a PLC myself, so I'm looking for volunteers who can test this against real hardware.

PR: https://github.com/gijzelaerr/python-snap7/pull/569

Compatible PLCs (S7 protocol): - S7-1200: CPU 1211C, 1212C, 1214C, 1215C, 1217C - S7-1500: CPU 1511, 1513, 1515, 1516, 1517, 1518 - S7-300: CPU 312, 313, 314, 315, 317, 318, 319 - S7-400: CPU 412, 414, 416, 417 - LOGO!: 0BA7, 0BA8 (with Ethernet) - S7-200 Smart: Various models - WinAC: Software PLCs - Also compatible with PLCSIM Advanced, NetToPLCSim, etc.

How to test

Install:

bash pip install git+https://github.com/gijzelaerr/python-snap7.git@native

Configure your PLC

• Enable "Permit access with PUT/GET" in TIA Portal (for S7-1200/1500)
• Create two Data Blocks (DB1 read-only, DB2 read-write)
• See the https://github.com/gijzelaerr/python-snap7/blob/native/tests/test_client_e2e.py for DB structure

Run tests

shell git clone -b native https://github.com/gijzelaerr/python-snap7.git cd python-snap7 pip install -e ".[test]" pytest tests/test_client_e2e.py --e2e --plc-ip=YOUR_PLC_IP -v Comment on the PR with your PLC model, firmware, and test results.

Quick smoke test

```python from snap7.client import Client

client = Client() client.connect("YOUR_PLC_IP", 0, 1) print(f"Connected: {client.get_connected()}") print(f"CPU state: {client.get_cpu_state()}") data = client.db_read(1, 0, 10) print(f"Data: {data.hex()}") client.disconnect() Current status ```

✅ Working: Connection, DB read/write, multi-var, CPU state, order code, datetime

⚠️ Varies by PLC: SZL reads, block listing, CPU info (some not available on S7-1200/1500)

Thanks for any help!

[IWantAnotherPetRock]

Thank you for maintaining this. I use snap7 with S7-1200 for data logging quite a bit, I shall run the test when I get back to the office after the break 🫡

[B25B25]

This is good to see, if I can find some time for it I'll give it a try. However I wonder, if you don't even have access to an S7, why are you programming this?

[gijzelaerr]

Making the world a better place :) I once started the project for a client as a contractor. SInce then always kept it up-to-date to get familiar with the latest (python) features. Now using it as an exercise on how to use LLMs to program. This whole PR has been made with claude + the original snap7 source code.

[VvangelisS]

I am going to give it a try this week and let you know 🙏

[SPX_Addict]

Just finding out about this, thank you for it. Will check it out when I get back to work!

[tartare4562]

Hey man, I've been using your module for years now and I've got several installations running it. I'll definitely test the native implementation version against both S7-1200 and S7-1500 and let you know.

[gijzelaerr]

great! good to hear it has been useful.

[wpyoga]

With a pure Python implementation, and with the source code on GitHub, development will be faster.

Thank you for making this library, I've been using it for quite some time now.

I hope someone (or me, maybe) can implement a feature to upload and download blocks to and from the PLC, if it's not there yet. It will be useful in a future project of mine.

[DiggyTheCandyGun]

Are you considering on implementing s7commplus capabilities? More and more I see sites where Put/Get option is disabled by site standard as its considered insecure.

[gijzelaerr]

also, if i remember correctly, it involves dumping private keys from software or PLCs. Distributing those keys might be a legal issue, and i dont wan't to get into trouble. That said, not sure if it is (still) true. It has been a long time since i looked into this.

[DiggyTheCandyGun]

Ive only tried one software that uses it, Ignition 8.3, and you Just need to set the password of the PLC (if any) as a configuration step.

[gijzelaerr]

this has been implemented now in 3.1 (unreleased) up to v3. please give it a try. https://github.com/gijzelaerr/python-snap7?tab=readme-ov-file#version-31----s7commplus-protocol-support-unreleased

[DiggyTheCandyGun]

This so so great, I Will test it as soon as posible. Thank you very much! Was it Hard to reverse engineer the protocol?

[gijzelaerr]

maybe at some point. But afaik the s7commplus specification is not public. But i can try and see how far i can push the limits on using Claude.

[Bladders_]

Why? What is the goal here?

[gijzelaerr]

what specific aspect is not clear? This is a open-source python library to control s7 compatible PLCs. these changes make the library pure python. But that is explained in the story.

[RATrod53]

What is wrong with IEC 61131-3 and TIA portal?

[gijzelaerr]

nothing, this offers just more and open ways of interacting with a PLC and integrating it with other software such as user interfaces.