Add note about mpdecimal requirement on some Unix platforms

[antonok-edm]

#25 (comment)

mpdecimal can't really be added as a dependency of RP2 since it's a system library rather than a Python package, but at least we can document it in the installation/setup instructions.

[antonok-edm]

Potentially, another option is to include a check like this during some initialization routine:

try:
    from _decimal import *
except ImportError:
    print(MPDECIMAL_NOT_AVAILABLE_WARNING)
    sys.exit(-1)

[eprbell]

Potentially, another option is to include a check like this during some initialization routine:

try:
    from _decimal import *
except ImportError:
    print(MPDECIMAL_NOT_AVAILABLE_WARNING)
    sys.exit(-1)

I think this is a good approach. It could go here: https://github.com/eprbell/rp2/blob/main/src/rp2/rp2_main.py#L70. The only changes needed are:

• use LOGGER.error instead of print;
• sys.exit(1) instead of -1;

Then I think we no longer need the changes to the README files.

[antonok-edm]

updated!

I also changed the import to as _ to avoid polluting the namespace.

[eprbell]

LGTM! I just suggested a comment to describe the issue. Also I think it's fine to disable the import-outside-toplevel pylint warning on the line where it occurs.

[eprbell]

Good stuff!