Implement platform_system in requirements.txt

[Neradoc]

Pip uses the following notation for platform-specific modules:

pywin32;platform_system=='Windows'
pyudev;platform_system=='Linux'

circup install -r would pick those as pywin32;platform_system, etc.

Would it be a good idea to:

• have circup find and read the platform_system parameter (and ignore the module)
• use a platform_system=='circuitpython' to specify modules that pip will ignore, but circup still install

This would allow pip and circup requirements to live in the same file to some extent for, say a project that is to be deployed on both a host and a target board. (For example circup itself can be a requirement for the host). Modules without a platform_system specified would still be installed (or ignored if known) as usual.

[chabala]

Thank you for writing this up @Neradoc

[Neradoc]

Interestingly since circup cuts the line at the == sign to ignore the version, this format works to have the module ignored by pip and installed by circup.

adafruit_datetime==0;platform_system=='circuitpython'

[askpatrickw]

There is an interesting and related discussion on my Gist from 2021 about how maybe (someday) you could use pip to install to circuitpython libraries onto boards.

https://gist.github.com/askpatrickw/e69eacd2c60c8e27f255d976ab5e8820