Provide typehints for payload classes and methods

[campbellmbrown]

Issue

It would be nice if the payload.py module had consistent typehinting to pass static linting tools (e.g. MyPy):

For example,

def decode_8bit_int(self):
def decode_16bit_int(self):
def decode_32bit_int(self):
def decode_64bit_int(self):

should be:

def decode_8bit_int(self) -> int:
def decode_16bit_int(self) -> int:
def decode_32bit_int(self) -> int:
def decode_64bit_int(self) -> int:

Note half of this module is already typehinted.

Reproduce

Set up environment:

$ python --version
Python 3.13.2

$ python -m venv .venv

$ .venv\Scripts\activate

$ pip install pymodbus mypy

$ pip list
Package           Version
----------------- -------
mypy              1.15.0
mypy-extensions   1.0.0
pip               24.3.1
pymodbus          3.8.6
typing_extensions 4.13.1

Basic example:

from pymodbus.payload import BinaryPayloadDecoder
from pymodbus.constants import Endian

decoder = BinaryPayloadDecoder(b"\x01\x02\x03\x04\x05\x06\x07\x08", byteorder=Endian.BIG)
print(decoder.decode_16bit_int())
print(decoder.decode_32bit_int())
print(decoder.decode_8bit_int())

Output:

$ mypy mypy_test.py --strict
mypy_test.py:4: error: Call to untyped function "BinaryPayloadDecoder" in typed context  [no-untyped-call]
mypy_test.py:5: error: Call to untyped function "decode_16bit_int" in typed context  [no-untyped-call]
mypy_test.py:6: error: Call to untyped function "decode_32bit_int" in typed context  [no-untyped-call]
mypy_test.py:7: error: Call to untyped function "decode_8bit_int" in typed context  [no-untyped-call]
Found 4 errors in 1 file (checked 1 source file)

Workaround

A MyPy specific workaround is to add # type: ignore[no-untyped-call] to each line, but this isn't ideal.

[janiversen]

payload.py will be removed in the next release, and is already gone on dev so it's hard to type hint.