Python Snap7 Easy Vars

A Python wrapper for the snap7 PLC communication library with easy variable management. This library simplifies reading and writing variables to Siemens PLCs using snap7 by allowing users to define data structures that map directly to PLC data blocks. It wraps around the python-snap7 library and provides an easy-to-use interface for defining PLC variables, reading from, and writing to the PLC.

Quick Start

Install the package via pip:

pip install python-snap7-easy-vars

Import the library and create a data structure:

import snap7_easy_vars

class MyPLCData(snap7_easy_vars.PLCData):
    # Define PLC variables with their data types and offsets
    temperature = snap7_easy_vars.PLCRealField(byte_offset=0) 
    pressure = snap7_easy_vars.PLCWordField(byte_offset=4)

    # By default, fields are read-only; to make a field settable, use the 'settable' parameter
    status = snap7_easy_vars.PLCBoolField(byte_offset=6, bit_offset=0, settable=True)

Connect to the PLC and read/write data:

my_plc_data = MyPLCData()
my_plc_connection = snap7_easy_vars.PLCConnection(
    ip_address="192.168.0.1", # PLC IP address
    data_store=my_plc_data,
    db_number=1, # PLC DB number
    rack=0, # PLC rack number
    slot=1, # PLC slot number
    port=102, # PLC port number
)

# Connect to the PLC
my_plc_connection.connect()

# Read data from the PLC
my_plc_connection.read()

# Read variables
print(f"Temperature: {my_plc_data.temperature}")
print(f"Pressure: {my_plc_data.pressure}")
print(f"Status: {my_plc_data.status}")

# Modify a variable and write back to the PLC
my_plc_data.status = True
my_plc_connection.write()

Authors

• Marvin Ruciński