Replace Float 'nan' with None for modbus floats

[String-656]

Proposed change

Detect NaN from modbus registers. Float 16/32/64 can return NaN 0x7FC0 which currently gets converted to a string, resulting in the core throwing an error as it's expecting a number. The PR detects 'nan' in unpack_structure_result, replacing with None

Type of change

• Dependency upgrade
• Bugfix (non-breaking change which fixes an issue)
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• New feature (which adds functionality to an existing integration)
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• Breaking change (fix/feature causing existing functionality to break)
• Code quality improvements to existing code or addition of tests

Additional information

• This PR fixes or closes issue:
  fixes Modbus - Exception since 2023.5.0: state class None: numeric value, however, it has the non-numeric value. #93297
• This PR is related to issue:
• Link to documentation pull request:

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[home-assistant]

Hey there @adamchengtkc, @janiversen, @vzahradnik, mind taking a look at this pull request as it has been labeled with an integration (modbus) you are listed as a code owner for? Thanks!

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[janiversen]

Test cases are missing, to verify your changes work.

[janiversen]

This looks wrong. this can never be true.

[String-656]

floats that equal NaN are never equal to itself. The array temp variable, "v_temp" and further down the "val_result" are floats. I will provide testing evidence showing the case when NaN is received.

[janiversen]

you test if the variable if different from the same variable.

If you look at the failing tests, pylint also mark this as an error.

[String-656]

Correct, that's one way of detecting NaN. See if it is equal to its self.
https://stackoverflow.com/questions/10034149/why-is-nan-not-equal-to-nan

[home-assistant]

Please take a look at the requested changes, and use the Ready for review button when you are done, thanks 👍

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[String-656]

I had a read of https://developers.home-assistant.io/docs/development_testing .. and I'm out of my depth.. I don't know where to start with creating sufficient test records.

Below is a test that shows that val_result != val_result is true when the registers for a float32 return 0x7FC0. I added a debug output to the code, as seen highlighted on the right.

New code when register is NaN...

New code returning val_result when float32 register is a normal number..

Additionally I see the pylint and mypy didn't pass above in the checks. The comparison to it's self is one way to detect NaN, but the the following line I don't know how to solve as the function is passing back a string list, where one of those float values COULD be a NaN... e.g. If unpack() returns a tuple greater than 1, and one of those registers is (0x7FC0)

base_platform.py:224: error: Argument 1 to "append" of "list" has incompatible type "None"; expected "str" [arg-type]

If you can't send 'None' in a str List, then I don't know what value you would put in there so that the core doesn't throw an error... Note I couldn't simulate a scenario where unpack() returns a tuple greater than 1. I would expect you might see that if you used Modbus Function Code 3, read multiple holding registers...

[janiversen]

look in the test directory and e.g. add it to the existing sensor tests. The modbus integration is proud of having 100% test coverage (all code lines are passed at least once in a test run) and we want to keep it that way.

[janiversen]

LGTM (with the extras)