--serial_device not working

[idegre]

when attempting to use the --serial_device parameter it always returns an error.
sorry I don't have the exact error as I changed the code on my pi and didn't get any screenshots or the exact error. I found this when trying to use a usb->serial interface on my pi3 so i wouldn't need to deal with the onboard serial
luckily its an easy fix, but i cant create a PR to save you the trouble
https://github.com/UedaTakeyuki/mh-z19/blob/master/pypi/mh_z19/__main__.py#L56 here it should be mh_z19.set_serialdevice(args.serial_device)

Describe the bug
when attempting to use the --serial_device parameter it always returns an error.
sorry I don't have the exact error as I changed the code on my pi and didn't get any screenshots

To Reproduce

1. call sudo python3 -m mh_z19 --serial_device /dev/ttyUSB0
2. see set_serialdevice(args.serial_device) is undefined error

Expected behavior
the command should work

Screenshots
If applicable, add screenshots to help explain your problem.

[UedaTakeyuki]

Hi, idegre!

I really appreciated your issue report.
The reported issue is reproduced on my side, so I think I can fix it soon.

[UedaTakeyuki]

Hi, idegre!

I've fixed it, now it works as follows:

pi@raspberrypi:~ $ sudo python -m mh_z19 --serial_device /dev/serial0
{"co2": 535}
pi@raspberrypi:~ $ sudo python -m mh_z19 --version
0.6.3

Please update your mh_z19 module and tell me the result, thx!

[UedaTakeyuki]

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