No longer able to specify unit type in read_holding_registers

[ohshazbot]

Versions

• Python: 3.9.14
• OS: Ubuntu 22.04LTS
• Pymodbus: 3.2.0
• Modbus Hardware (if used): N/A

Pymodbus Specific

• Server: N/A
• Client: N/A

Description

I'm upgrading some code from 2.5.3 to 3.x and bumped into this bug. Looks like when units were added, they were not prepared for units coming in as kwargs, resulting in

Traceback (most recent call last):
  File "/home/john/workspace/collection/modbus/test.py", line 5, in <module>
    client.read_holding_registers(address=0, unit='VAH', count=1)
  File "/home/john/.pyenv/versions/3.9.14/envs/collection-modbus/lib/python3.9/site-packages/pymodbus/client/mixin.py", line 104, in read_holding_registers
    pdu_reg_read.ReadHoldingRegistersRequest(address, count, slave, **kwargs)
TypeError: __init__() got multiple values for argument 'unit'

read_holding_registers does not expose unit as an explicit argument so kwargs is the only option. Similar problems look like they exist in most of the functions in the client/mixin.py.

It's also totally possible that I'm doing something wrong, my Python isn't that great.

Code and Logs

from pymodbus.client import AsyncModbusTcpClient

client = AsyncModbusTcpClient(host='localhost', port=502)
client.connect()
client.read_holding_registers(address=0, unit='VAH', count=1)

[janiversen]

unit was never meant to be something about how to interpret the values ( celcius, var etc...) it was the slave id and still is.

when you upgrade you will see that most unit= have been changed to slave=

[janiversen]

rIf you used unit='VAN' you are lucky if it worked, it is probably interpreted as unit=0 meaning any slave.