Don't raise ImportError on non-linux platforms

[asottile]

In order to be able to use distro in cross-platform programs without duplicated import guards, distro shouldn't raise on import.

For what it's worth, after this patch distro acts mostly in the same way as platform.linux_distribution on non-linux platforms:

>>> platform.linux_distribution()
('', '', '')
>>> distro.id(), distro.version(), distro.codename()
('', '', '')

[asottile]

This will fix my patch here on non-linux platforms: asottile-archive/pip-custom-platform#15

[nir0s]

The reason this was added is partly because platform.linux_distribution returns empty when it doesn't know how to identify the distro it's running on. In a Windows/Darwin case, it's not that we can't identify it, it's just that it's not supposed to.

[asottile]

I think that's fine, at the very least it's the status quo for the platform module.

This patch makes using distro in a cross platform way much easier and definitely makes migrating from old platform-based code dead simple.

[nir0s]

@asottile btw, it would be awesome to get your feedback on https://github.com/cloudify-cosmo/wagon.

[asottile]

@nir0s looks pretty neat! Seems to be trying to solve the same problems as pip-custom-platform too.

I'd be curious to see the full workflow of how wagon gets used -- for pip-custom-platform it's largely:

• build wheels for all supported platform combinations for all supported packages
• place those wheels on an internal pypi server
• s/pip/pip-custom-platform/g in installation scripts