Pure native python snap7

[gijzelaerr]

Pure Python S7 Protocol Implementation

This PR replaces the C library (Snap7) dependency with a pure Python implementation of the S7 protocol.

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.

Compatible PLCs (S7 protocol)

If you have any of these, we'd love your help:

Series	Models
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 S7 protocol simulators like PLCSIM Advanced, NetToPLCSim, etc.

How to test

1. Install the test version

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

2. Configure your PLC

• Enable "Permit access with PUT/GET" in TIA Portal (for S7-1200/1500)
• Create two Data Blocks:
  • DB1 "Read_only" with test values
  • DB2 "Read_write" for write tests
• See the test file header for the exact DB structure

3. Run the tests

# Clone the repo
git clone -b native https://github.com/gijzelaerr/python-snap7.git
cd python-snap7

# Install with test dependencies
pip install -e ".[test]"

# Run e2e tests with your PLC settings
pytest tests/test_client_e2e.py --e2e \
    --plc-ip=YOUR_PLC_IP \
    --plc-rack=0 \
    --plc-slot=1 \
    -v --html=report.html

Available options:

Option	Default	Description
--e2e	(required)	Enable e2e tests
--plc-ip	10.10.10.100	PLC IP address
--plc-rack	0	Rack number
--plc-slot	1	Slot number
--plc-port	102	TCP port
--plc-db-read	1	Read-only DB number
--plc-db-write	2	Read-write DB number

4. Share your results

Please comment on this PR with:

• Your PLC model and firmware version
• Which tests passed/failed
• The HTML report if possible

Quick smoke test

If you just want to do a quick test:

from snap7.client import Client

client = Client()
client.connect("YOUR_PLC_IP", 0, 1)  # IP, rack, slot
print(f"Connected: {client.get_connected()}")
print(f"CPU state: {client.get_cpu_state()}")

# Read 10 bytes from DB1 at offset 0
data = client.db_read(1, 0, 10)
print(f"Data: {data.hex()}")

client.disconnect()

Current status

✅ Working:

• Connection/disconnection
• DB read/write (all data types)
• Multi-var read/write
• CPU state, PDU length
• Order code, PLC datetime

⚠️ May vary by PLC model:

• SZL reads (some IDs not available on S7-1200/1500)
• Block listing
• CPU info

---

Thanks for any help! Every test against real hardware helps make this library better.

[lupaulus]

Needs to be reworked and reviewed with real tests

[gijzelaerr]

it would be more useful if the comment was a bit more specific.

[gijzelaerr]

meanwhile i found a couple of problems where the AI has fooled me (implement fake calls in the client), i'm fixing those now.

[lupaulus]

Yeah IA is great to start but then you need to review it because she is "lazy" and don't do the task entirely

[gijzelaerr]

This should be in a better shape now.