pylogix

1.1.5 verified Fri May 01 auth: no python

pylogix is a Python library for reading and writing Rockwell Automation Logix-based PLCs (ControlLogix, CompactLogix, MicroLogix, etc.) over Ethernet/IP. Current version is 1.1.5, released occasionally with bug fixes and minor enhancements.

pip install pylogix

Common errors

error AttributeError: module 'pylogix' has no attribute 'read' ↓

cause Using old import 'from pylogix import read' after upgrading to version >=0.7.0.

fix

Use 'from pylogix import PLC' and then call plc.Read() instead.

error pylogix.exceptions.ConnectionError: Unable to connect to the PLC ↓

cause Incorrect IP address, PLC not reachable, or wrong CIP path.

fix

Verify IP address, ensure PLC is on the same subnet, and check firewall settings. If using a ControlLogix, set comm.ProcessorSlot if not 0.

error pylogix.exceptions.TagError: Tag Not Found ↓

cause Tag name does not exist or incorrect path (e.g., missing program scope).

fix

Use the exact tag path including program scope (e.g., 'Program:MainProgram.MyTag') and confirm case sensitivity.

Warnings

gotcha The PLC object modifies its internal state (like IPAddress) after each read/write call. Always set IPAddress before each transaction or use a context manager. ↓

fix Set comm.IPAddress immediately before calling Read/Write, or use 'with PLC() as comm:' which resets on exit.

gotcha Tag names must be exact and case-sensitive. Rockwell PLCs often require the full path (e.g., 'Program:MainProgram.MyTag'). ↓

fix Verify tag name in the PLC’s tag database; use the full path including program scope if needed.

breaking Version 0.7.0 changed the API: 'read' and 'write' functions were replaced by methods on the PLC object. Old code using 'from pylogix import read' breaks. ↓

fix Update to use 'from pylogix import PLC' and instantiate PLC() object, then call .Read() and .Write().

Imports

PLC
```
from pylogix import PLC
```
Correct import for the PLC class.

Quickstart

Basic read operation: initialize PLC, set IP, read a tag, and print the value.

from pylogix import PLC

with PLC() as comm:
    comm.IPAddress = '192.168.1.10'
    ret = comm.Read('MyTag')
    if ret.Value is not None:
        print(ret.Value)